Patent Publication Number: US-2023149651-A1

Title: Patient interface

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/710,216, filed Dec. 11, 2019, now allowed, which is a continuation of U.S. application Ser. No. 14/760,808, filed Jul. 14, 2015, now U.S. Pat. No. 10,543,332, which is the U.S. national phase of International Application No. PCT/AU2014/000026, filed Jan. 16, 2014, which designated the U.S. and claims the benefit of US Provisional Appln. No. 61/904,974, filed Nov. 15, 2013, 61/817,674, filed Apr. 30, 2013, 61/823,192, filed May 14, 2013, 61/823,353, filed May 14, 2013, 61/837,521, filed Jun. 20, 2013, and 61/839,916, filed Jun. 27, 2013. This application claims the benefit of Australian Provisional Appln. Nos. 2013900132, filed Jan. 16, 2013, and 2013900168, filed Jan. 18, 2013. This application claims the benefit of New Zealand Appln. Nos. 605907, filed Jan. 16, 2013, each of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE TECHNOLOGY 
     (1) Field of the Technology 
     The present technology relates to one or more of the diagnosis, treatment and amelioration of respiratory disorders, and to procedures to prevent respiratory disorders. In particular, the present technology relates to medical devices, and their use for treating respiratory disorders and for preventing respiratory disorders. 
     (2) Description of the Related Art 
     The respiratory system of the body facilitates gas exchange. The nose and mouth form the entrance to the airways of a patient. 
     The airways include a series of branching tubes, which become narrower, shorter and more numerous as they penetrate deeper into the lung. The prime function of the lungs is gas exchange, allowing oxygen to move from the air into the venous blood and carbon dioxide to move out. The trachea divides into right and left main bronchi, which further divide eventually into terminal bronchioles. The bronchi make up the conducting airways, and do not take part in gas exchange. Further divisions of the airways lead to the respiratory bronchioles, and eventually to the alveoli. The alveolated region of the lung is where the gas exchange takes place, and is referred to as the respiratory zone. 
     A range of respiratory disorders exist. 
     Obstructive Sleep Apnoea (OSA), a form of Sleep Disordered Breathing (SDB), is characterized by occlusion of the upper air passage during sleep. It results from a combination of an abnormally small upper airway and the normal loss of muscle tone in the region of the tongue, soft palate and posterior oropharyngeal wall during sleep. The condition causes the affected patient to stop breathing for periods typically of 30 to 120 seconds duration, sometimes 200 to 300 times per night. It often causes excessive daytime somnolence, and it may cause cardiovascular disease and brain damage. The syndrome is a common disorder, particularly in middle aged overweight males, although a person affected may have no awareness of the problem. See U.S. Pat. No. 4,944,310 (Sullivan). 
     Cheyne-Stokes Respiration (CSR) is a disorder of a patient&#39;s respiratory controller in which there are rhythmic alternating periods of waxing and waning ventilation, causing repetitive de-oxygenation and re-oxygenation of the arterial blood. It is possible that CSR is harmful because of the repetitive hypoxia. In some patients CSR is associated with repetitive arousal from sleep, which causes severe sleep disruption, increased sympathetic activity, and increased afterload. See U.S. Pat. No. 6,532,959 (Berthon-Jones). 
     Obesity Hyperventilation Syndrome (OHS) is defined as the combination of severe obesity and awake chronic hypercapnia, in the absence of other known causes for hypoventilation. Symptoms include dyspnea, morning headache and excessive daytime sleepiness. 
     Chronic Obstructive Pulmonary Disease (COPD) encompasses any of a group of lower airway diseases that have certain characteristics in common. These include increased resistance to air movement, extended expiratory phase of respiration, and loss of the normal elasticity of the lung. Examples of COPD are emphysema and chronic bronchitis. COPD is caused by chronic tobacco smoking (primary risk factor), occupational exposures, air pollution and genetic factors. Symptoms include: dyspnea on exertion, chronic cough and sputum production. 
     Neuromuscular Disease (NMD) is a broad term that encompasses many diseases and ailments that impair the functioning of the muscles either directly via intrinsic muscle pathology, or indirectly via nerve pathology. Some NMD patients are characterised by progressive muscular impairment leading to loss of ambulation, being wheelchair-bound, swallowing difficulties, respiratory muscle weakness and, eventually, death from respiratory failure. Neuromuscular disorders can be divided into rapidly progressive and slowly progressive: (i) Rapidly progressive disorders: Characterised by muscle impairment that worsens over months and results in death within a few years (e.g. Amyotrophic lateral sclerosis (ALS) and Duchenne muscular dystrophy (DMD) in teenagers); (ii) Variable or slowly progressive disorders: Characterised by muscle impairment that worsens over years and only mildly reduces life expectancy (e.g. Limb girdle, Facioscapulohumeral and Myotonic muscular dystrophy). Symptoms of respiratory failure in NMD include: increasing generalised weakness, dysphagia, dyspnea on exertion and at rest, fatigue, sleepiness, morning headache, and difficulties with concentration and mood changes. 
     Chest wall disorders are a group of thoracic deformities that result in inefficient coupling between the respiratory muscles and the thoracic cage. The disorders are usually characterised by a restrictive defect and share the potential of long term hypercapnic respiratory failure. Scoliosis and/or kyphoscoliosis may cause severe respiratory failure. Symptoms of respiratory failure include: dyspnea on exertion, peripheral oedema, orthopnoea, repeated chest infections, morning headaches, fatigue, poor sleep quality and loss of appetite. 
     Otherwise healthy individuals may take advantage of systems and devices to prevent respiratory disorders from arising. 
     Systems 
     One known product used for treating SDB is the S9 Sleep Therapy System, manufactured by ResMed. 
     Therapy 
     Nasal Continuous Positive Airway Pressure (CPAP) therapy has been used to treat Obstructive Sleep Apnea (OSA). The hypothesis is that continuous positive airway pressure acts as a pneumatic splint and may prevent upper airway occlusion by pushing the soft palate and tongue forward and away from the posterior oropharyngeal wall. 
     Non-invasive ventilation (NIV) has been used to treat OHS, COPD, MD and Chest Wall disorders. 
     Patient Interface 
     The application of a supply of air at positive pressure to the entrance of the airways of a patient is facilitated by the use of a patient interface, such as a nasal mask, full-face mask, nasal pillows or a nasal cradle mask. A full-face mask includes a mask with one sealing-forming portion covering at least the nares and mouth, or more than one sealing-forming portion to individually cover at least the nares and mouth. A range of patient interface devices are known, however a number of them suffer from being one or more of obtrusive, aesthetically undesirable, poorly fitting, difficult to use and uncomfortable especially when worn for long periods of time or when a patient is unfamiliar with a system. Masks designed solely for aviators, as part of personal protection equipment or for the administration of anaesthetics may be tolerable for their original application, but nevertheless be undesirably uncomfortable to be worn for extended periods, for example, while sleeping. 
     Seal-Forming Structure 
     Patient interfaces typically include a seal-forming structure. 
     One type of seal-forming structure extends around the periphery of the patient interface, and is intended to seal against the user&#39;s face when force is applied to the patient interface with the seal-forming structure in confronting engagement with the user&#39;s face. The seal-forming structure may include an air or fluid filled cushion, or a moulded or formed surface of a resilient seal element made of an elastomer such as a rubber. With this type of seal-forming structure, if the fit is not adequate, there will be gaps between the seal-forming structure and the face, and additional force will be required to force the patient interface against the face in order to achieve a seal. 
     Another type of seal-forming structure incorporates a flap seal of thin material so positioned about the periphery of the mask so as to provide a self-sealing action against the face of the user when positive pressure is applied within the mask. Like the previous style of seal-forming structure, if the match between the face and the mask is not good, additional force may be required to effect a seal, or the mask may leak. Furthermore, if the shape of the seal-forming structure does not match that of the patient, it may crease or buckle in use, giving rise to leaks. 
     Another form of seal-forming structure may use adhesive to affect a seal. Some patients may find it inconvenient to constantly apply and remove an adhesive to their face. 
     A range of patient interface seal-forming structure technologies are disclosed in the following patent applications, assigned to ResMed Limited: WO 1998/004,310; WO 2006/074,513; WO 2010/135,785. 
     Positioning and Stabilising 
     A seal-forming structure of a patient interface used for positive air pressure therapy is subject to the corresponding force of the air pressure to disrupt a seal. Thus a variety of techniques have been used to position the seal-forming structure, and to maintain it in sealing relation with the appropriate portion of the face. 
     One technique is the use of adhesives. See for example US Patent publication US 2010/0000534. 
     Another technique is the use of one or more straps and stabilising harnesses. Many such harnesses suffer from being one or more of ill-fitting, bulky, uncomfortable and awkward to use. 
     Rigid elements, also known as “rigidisers”, have been used with stretchable headgears previously. One known problem is associated with the fact that a rigidiser permanently attached (e.g. laminated or stitched) to a large area of the stretchable material limits the stretchable length of the material, thus affecting the elastic properties of the entire headgear. Another issue concerns cleaning the headgear which would require both the rigidiser and stretchable material to be washed together as they are permanently attached to each other. 
     Vent Technologies 
     Some forms of patient interface systems may include a vent to allow the washout of exhaled carbon dioxide. Many such vents are noisy. Others may block in use and provide insufficient washout. Some vents may be disruptive of the sleep of a bed-partner of the patient, e.g. through noise or focused airflow. Some vents cannot be properly cleaned and must be discarded after they become blocked. Some vents are intended to be used for a short duration of time, i.e. less than three months, and therefore are manufactured from fragile material to prevent washing or frequent washing so as to encourage more frequent replacement of the vent. ResMed Limited has developed a number of improved mask vent technologies. See WO 1998/034,665; WO 2000/078,381; U.S. Pat. No. 6,581,594; US Patent Application; US 2009/0050156; US Patent Application 2009/0044808. 
     
       
         
           
               
            
               
                   
               
               
                 Table of noise of prior masks (ISO 17510-2:2007, 10 cmH 2 O pressure at 1 m) 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 A-weighted 
                 A-weighted 
                   
               
               
                   
                   
                 sound power 
                 sound 
                   
               
               
                   
                   
                 level dbA 
                 pressure dbA 
                 Year 
               
               
                 Mask name 
                 Mask type 
                 (uncertainty) 
                 (uncertainty) 
                 (approx.) 
               
               
                   
               
               
                 Glue-on (*) 
                 nasal 
                 50.9 
                 42.9 
                 1981 
               
               
                 ResCare standard (*) 
                 nasal 
                 31.5 
                 23.5 
                 1993 
               
               
                 ResMed Mirage (*) 
                 nasal 
                 29.5 
                 21.5 
                 1998 
               
               
                 ResMed UltraMirage 
                 nasal 
                 36 (3) 
                 28 (3) 
                 2000 
               
               
                 ResMed Mirage Activa 
                 nasal 
                 32 (3) 
                 24 (3) 
                 2002 
               
               
                 ResMed Mirage Micro 
                 nasal 
                 30 (3) 
                 22 (3) 
                 2008 
               
               
                 ResMed Mirage SoftGel 
                 nasal 
                 29 (3) 
                 22 (3) 
                 2008 
               
               
                 ResMed Mirage FX 
                 nasal 
                 26 (3) 
                 18 (3) 
                 2010 
               
               
                 ResMed Mirage Swift (*) 
                 nasal pillows 
                 37 
                 29 
                 2004 
               
               
                 ResMed Mirage Swift II 
                 nasal pillows 
                 28 (3) 
                 20 (3) 
                 2005 
               
               
                 ResMed Mirage Swift LT 
                 nasal pillows 
                 25 (3) 
                 17 (3) 
                 2008 
               
               
                 ResMed Swift FX 
                 nasal pillows 
                 25 (3) 
                 17 (3) 
                 2011 
               
               
                 ResMed Mirage series 1.11 (*) 
                 full face 
                 31.7 
                 23.7 
                 2000 
               
               
                 ResMed UltraMirage 
                 full face 
                 35 (3) 
                 27 (3) 
                 2004 
               
               
                 ResMed Mirage Quattro 
                 full face 
                 26 (3) 
                 18 (3) 
                 2006 
               
               
                 ResMed Mirage Quattro FX 
                 full face 
                 27 (3) 
                 19 (3) 
                 2008 
               
               
                   
               
               
                 (* one specimen only, measured using test method specified in ISO3744 in CPAP mode at 10 cmH 2 O) 
               
            
           
         
       
     
     
       
         
           
               
            
               
                   
               
               
                 Sound pressure values of a variety of objects are listed below 
               
            
           
           
               
               
               
            
               
                   
                 A-weighted sound  
                   
               
               
                   
                 pressure dbA  
                   
               
               
                 Object 
                 (uncertainty) 
                 Notes 
               
               
                   
               
               
                 Vacuum cleaner: Nilfisk 
                 68 
                 ISO3744 at 1 m 
               
               
                 Walter Broadly Litter Hog:  
                   
                 distance 
               
               
                 B+ Grade 
                   
                   
               
               
                 Conversational speech 
                 60 
                 1 m distance 
               
               
                 Average home 
                 50 
                   
               
               
                 Quiet library 
                 40 
                   
               
               
                 Quiet bedroom at night 
                 30 
                   
               
               
                 Background in TV studio 
                 20 
               
               
                   
               
            
           
         
       
     
     Nasal Pillow Technologies 
     One form of nasal pillow is found in the Adam Circuit manufactured by Puritan Bennett. Another nasal pillow, or nasal puff is the subject of U.S. Pat. No. 4,782,832 (Trimble et al.), assigned to Puritan-Bennett Corporation. 
     ResMed Limited has manufactured the following products that incorporate nasal pillows: SWIFT™ nasal pillows mask, SWIFT II™ nasal pillows mask, SWIFT LT™ nasal pillows mask, SWIFT FX™ nasal pillows mask and LIBERTY full-face mask. The following patent applications, assigned to ResMed Limited, describe nasal pillows masks: International Patent Application WO2004/073,778 (describing amongst other things aspects of ResMed SWIFT™ nasal pillows), US Patent Application 2009/0044808 (describing amongst other things aspects of ResMed SWIFT LT nasal pillows); International Patent Applications WO 2005/063,328 and WO 2006/130,903 (describing amongst other things aspects of ResMed LIBERTY™ full-face mask); International Patent Application WO 2009/052,560 (describing amongst other things aspects of ResMed SWIFT FX™ nasal pillows). 
     PAP Device 
     The air at positive pressure is typically supplied to the airway of a patient by a PAP device such as a motor-driven blower. The outlet of the blower is connected via a flexible delivery conduit to a patient interface as described above. 
     Mandibular Repositioning 
     A mandibular repositioning device (MRD) is one of the treatment options for sleep apnea. It is a custom made, adjustable oral appliance available from a dentist that holds the lower jaw in a forward position during sleep. This mechanical protrusion expands the space behind the tongue, puts tension on the pharyngeal walls to reduce collapse of the airway and diminishes palate vibration. 
     BRIEF SUMMARY OF THE TECHNOLOGY 
     The present technology is directed towards providing medical devices used in the diagnosis, amelioration, treatment, or prevention of respiratory disorders having one or more of improved comfort, cost, efficacy, ease of use and manufacturability. 
     One aspect of the present technology relates to apparatus used in the diagnosis, amelioration, treatment or prevention of a respiratory disorder. 
     Another aspect of the present technology relates to methods used in the diagnosis, amelioration, treatment or prevention of a respiratory disorder. 
     One aspect of one form of the present technology is a patient interface with a seal-forming structure that is removable for cleaning. It is the desire of the present technology to provide a patient interface that is light-weight compared to prior art patient interfaces, more unobtrusive compared to prior art patient interfaces and more quiet in use compared to prior art patient interfaces. It is also desirable to provide a patient interface that is intuitive to a patient when connecting mask components prior to commencement of therapy and is also simple to adjust and wear for therapy. 
     An aspect of one form of the present technology is a patient interface having a seal-forming structure that is locatable in position on the patient interface via a hard-to-hard connection. Another aspect of one form of the present technology is seal-forming structure of a patient interface that is removable for cleaning without requiring disconnection of a headgear portion of the patient interface. 
     An aspect of one form of the present technology is a patient interface comprising a seal-forming structure, a plenum chamber and a connection portion, wherein the seal-forming structure and the plenum chamber are formed from a relatively soft material, and the connection portion is formed from relatively rigid material. In one form the connection portion is removably connectable to a frame of the patient interface, e.g. via a snap-action, toggle or bi-stable mechanism. In one form the connection portion is insert moulded to the plenum chamber. 
     Another aspect of one form of the present technology is a patient interface that is moulded or otherwise constructed with a clearly defined perimeter shape which is intended to match that of an intended wearer (i.e. patient) and be intimate and conform with the face of the intended wearer. 
     An aspect of one form of the present technology is a method of manufacturing the patient interface described herein. It is a desire of the present technology to provide a method of manufacture that has less complexity than methods of manufacturing prior art patient interfaces to increase manufacturing efficiency, uses fewer raw materials and requires less assembly time by operators. 
     Another aspect of the present technology is directed to a patient interface for delivery of a supply of pressurised air or breathable gas to an entrance of a patient&#39;s airways. The patient interface may comprise: a cushion member that includes a retaining structure and a seal-forming structure permanently connected to the retaining structure; and a frame member, wherein the retaining structure and the frame member are repeatedly removably attachable to one another, wherein a gas chamber is formed at least in part by engagement of the cushion member and the frame member; and wherein an increase in air pressure within the cushion member causes a sealing force between the seal-forming structure and the frame member to increase. 
     An aspect of one form of the present technology is a method of manufacturing the patient interface. 
     Another aspect of the present technology is directed to a patient interface to deliver pressurized gas to a patient to treat sleep disordered breathing. The patient interface may comprise: a seal-forming structure having a nasal opening to provide pressurized gas to both nares of the patient and a plenum chamber formed in one piece, the plenum chamber including a plenum connection region, and the seal-forming structure is configured to seal around an inferior periphery of the patient&#39;s nose and below the bridge of the nose; a frame releasably attachable to the plenum connection region; a connection port formed in one piece with the frame; and a gas delivery tube permanently joined to the frame at the connection port, the gas delivery tube may comprise: a helical coil comprised of a plurality of adjacent coils, each coil separated by a width and having an outer surface defining a coil diameter; and a web of material coaxial to the helical coil attached to the helical coil between adjacent ones of the plurality of adjacent coils and having at least one fold extending radially outward between adjacent ones of the plurality of adjacent coils, said at least one fold defined by a predetermined fold line. 
     In examples, (a) a vertex of said at least one fold may define a fold diameter, (b) when the gas delivery tube is in a neutral state the coil diameter may be substantially equal to the fold diameter and the adjacent coils may be separated from each other in the neutral state, (c) the gas delivery tube may comprise one of three different states: a neutral state wherein the gas delivery tube comprises a neutral length, an extended state wherein the gas delivery tube is extended along its longitudinal axis to an extended length that is greater than the neutral length, and a compressed state wherein the gas delivery tube is compressed along its longitudinal axis to a compressed length that is less than the neutral length, (d) the web of material may comprise the at least one fold extending radially outward along at least one lengthwise portion of the gas delivery tube, (e) the web of material may have a slope angle that increases from the helical coil to the vertex of the at least one fold when the gas delivery tube is in the neutral state, (f) the web of material may have an asymmetrical cross-sectional profile about the predetermined fold line, (g) the predetermined fold line may be spaced evenly between adjacent ones of the plurality of adjacent coils, (h) the width separating adjacent ones of the plurality of adjacent coils may be substantially equal to a width of the helical coil when the gas delivery tube is in the neutral state, (i) the helical coil may comprise a greater proportion of a superficial surface area of the gas delivery tube than the at least one fold of the web of material, (j) an outer portion of the helical coil may have a rounded profile, (k) the helical coil may have a greater thickness than the web of material, (l) the web of material may have a substantially uniform thickness, (m) the helical coil may comprise a thermoplastic elastomer (TPE) or thermoplastic polyurethane (TPU) and/or the web of material may comprise a thermoplastic elastomer (TPE) or thermoplastic polyurethane (TPU), (n) the gas delivery tube may be permanently joined to the frame at the connection port by insert molding the frame to the gas delivery tube, (o) the web of material and the helical coil may be bonded to form a uniform and continuous inner surface of the gas delivery tube, (p) the at least one fold may extend radially outward between alternating ones of the plurality of adjacent coils, (q) said seal-forming structure may include a recessed portion to receive the tip of the nose of the patient, (r) a compliant region may be located above the recessed portion, said compliant region being thin and flexible relative to the remainder of the seal-forming structure, (s) said seal-forming structure may comprise foam, gel, and/or low durometer silicone, (t) said seal-forming structure may have a varied thickness around said nasal opening at predetermined positions, (u) said seal-forming structure may comprise a pair of protruding ends extending symmetrically about the nasal opening, each protruding end may be configured to seal against a region of the patient&#39;s face where the ala of the nose joins to the patient&#39;s face, (v) said seal-forming structure may comprise a pair of protruding end support sections corresponding to each protruding end and structured to support each protruding end and said pair of protruding end support sections may extend into a gas chamber defined at least in part by the seal-forming structure, (w) a lower portion of said seal-forming structure may be concave in a relaxed state to seal against the upper lip of the patient and to follow a curvature of the upper lip of the patient, and/or (x) the seal-forming structure may comprise a dual wall cushion to prevent collapse of the seal-forming structure when the seal-forming structure is engaged with the nose of the patient to form a pneumatic seal. 
     Another aspect of the present technology is directed to a patient interface to deliver pressurized gas to a patient to treat sleep disordered breathing. The patient interface may comprise: a seal-forming structure having a nasal opening to provide pressurized gas to both nares of the patient and a plenum chamber formed in one piece, the plenum chamber including a plenum connection region, and the seal-forming structure is configured to seal around an inferior periphery of the patient&#39;s nose and below the bridge of the nose; a frame releasably attachable to the plenum connection region, said frame comprising a first material; and a pair of rigidiser arms comprising a second material, said second material being different from said first material, wherein said frame and said pair of rigidiser arms are permanently connected. 
     In examples, (a) the first material may be relatively more resiliently flexible than the second material, (b) the frame may be overmolded to the pair of rigidiser arms to form a mechanical interlock, (c) the mechanical interlock may comprise an enclosable section extending from each of the pair of rigidiser arms that is overmolded by the material of the frame, (d) the enclosable section may have a hook and a portion of a bend, (e) the first material may be unable to be integrally bonded with the second material, (f) the first material may be a thermoplastic polyester elastomer and the second material may be a thermoplastic polymer, (g) the thermoplastic polymer may be polypropylene (PP), (h) the first material may be a fiber reinforced composite polypropylene material and the second material may be polypropylene, (i) each of the pair of rigidiser arms may include a protruding end configured to retain a pocketed end of a strap of a positioning and stabilising structure, and the protruding end may be proximal to the frame, (j) the first material may not be stretchable, and each of the pair of rigidiser arms may be structured such that it is more flexible in a plane substantially parallel to a patient&#39;s Frankfort horizontal compared to other planes, (k) each of the rigidiser arms may comprise: a main body having a curvature to substantially follow a cheek shape of a patient; and a connection portion configured to connect to the frame, the connection portion located at a distal end of the rigidiser arm, (l) the connection portion may comprise at least one protrusion and at least one void configured to be overmolded to connect to the frame, (m) said seal-forming structure may include a recessed portion to receive the tip of the nose of the patient, (n) a compliant region may be located above the recessed portion, said compliant region being thin and flexible relative to the remainder of the seal-forming structure, (o) said seal-forming structure may comprise foam, gel, and/or low durometer silicone, (p) said seal-forming structure may have a varied thickness around said nasal opening at predetermined positions, (q) said seal-forming structure may comprise a pair of protruding ends extending symmetrically about the nasal opening, each protruding end may be configured to seal against a region of the patient&#39;s face where the ala of the nose joins to the patient&#39;s face, (r) said seal-forming structure may comprise a pair of protruding end support sections corresponding to each protruding end and structured to support each protruding end and said pair of protruding end support sections may extend into a gas chamber defined at least in part by the seal-forming structure, (s) a lower portion of said seal-forming structure may be concave in a relaxed state to seal against the upper lip of the patient and to follow a curvature of the upper lip of the patient, and/or (t) the seal-forming structure may comprise a dual wall cushion to prevent collapse of the seal-forming structure when the seal-forming structure is engaged with the nose of the patient to form a pneumatic seal. 
     Another aspect of the present technology is directed to a patient interface to deliver pressurized gas to a patient to treat sleep disordered breathing. The patient interface may comprise: a seal-forming structure having a nasal opening to provide pressurized gas to both nares of the patient and a plenum chamber formed in one piece, the plenum chamber including a plenum connection region, and the seal-forming structure is configured to seal around an inferior periphery of the patient&#39;s nose and below the bridge of the nose; a frame releasably attachable to the plenum connection region; a connection port formed in one piece with the frame; and at least one vent to washout exhaled air, the vent permanently connected to the frame, wherein the at least one vent is made from a textile formed by interlacing plastic fibers, the textile having a predetermined amount of porosity. 
     In examples, (a) the at least one vent may comprise two vents permanently connected to the frame on opposite sides of the connection port, (b) the two vents may comprise a first vent having a first airflow rate and a second vent having a second airflow rate different from the first airflow rate, (c) the first airflow rate and the second airflow rate may be selected such that an average airflow rate of the first airflow rate and the second airflow rate is within a predetermined range, (d) the first airflow rate and/or the second airflow rate may be obtained by heat staking a portion of the first vent and/or the second vent, respectively, to the predetermined amount of porosity, (e) the plastic fibers may be made from a thermoplastic polymer from any one of the group consisting of: polypropylene, a woven polypropylene material, polycarbonate, nylon and polyethylene, (f) the at least one vent may be permanently connected to the frame by molecular adhesion using any one of the group consisting of: overmolding, co-injection molding and two shot (2K) injection molding, (g) the at least one vent may comprise a semi-circle shape or D-shape, (h) said seal-forming structure may include a recessed portion to receive the tip of the nose of the patient, (i) a compliant region may be located above the recessed portion, said compliant region being thin and flexible relative to the remainder of the seal-forming structure, (j) said seal-forming structure may comprise foam, gel, and/or low durometer silicone, (k) said seal-forming structure may have a varied thickness around said nasal opening at predetermined positions, (l) said seal-forming structure may comprise a pair of protruding ends extending symmetrically about the nasal opening, each protruding end may be configured to seal against a region of the patient&#39;s face where the ala of the nose joins to the patient&#39;s face, (m) said seal-forming structure may comprise a pair of protruding end support sections corresponding to each protruding end and structured to support each protruding end and said pair of protruding end support sections may extend into a gas chamber defined at least in part by the seal-forming structure, (n) a lower portion of said seal-forming structure may be concave in a relaxed state to seal against the upper lip of the patient and to follow a curvature of the upper lip of the patient, and/or (o) the seal-forming structure may comprise a dual wall cushion to prevent collapse of the seal-forming structure when the seal-forming structure is engaged with the nose of the patient to form a pneumatic seal. 
     Another aspect of the present technology is directed to a positioning and stabilising structure for a patient interface device. The positioning and stabilising structure may comprise: at least one strap; and at least one rigidiser arm, the at least one rigidiser arm including a main body and an extension to connect the main body to a mask frame, wherein the positioning and stabilising structure is arranged to position the at least one strap and the at least one rigidiser arm with regard to one another such that the at least one rigidiser arm imparts a predetermined shape to the at least one strap at a rigidised portion of the at least one strap and allowing at least the rigidised portion of the at least one strap to move relative to the at least one rigidiser arm, and said extension may be configured to prevent movement of the at least one rigidiser arm relative to the mask frame in a plane parallel with the patient&#39;s sagittal plane. 
     In examples, (a) the at least one rigidiser arm may be affixed to the at least one strap at one localized point or area only, (b) the at least one rigidiser arm may be affixed to the at least one strap in a limited area of the at least one strap, (c) the limited area may be adjacent a pocket or a sleeve opening of the at least one strap, (d) the at least one rigidiser arm may be multi-axially deformable to conform to a patient&#39;s facial profile, (e) the at least one rigidiser arm may be shaped to extend from a mask frame to a position proximally on or below the patient&#39;s cheekbone, (f) the at least one rigidiser arm may have a side profile that is crescent shaped, (g) an end portion of the at least one rigidiser arm may be affixed to the at least one strap, (h) the at least one rigidiser arm may be affixed to the at least one strap by sewing, welding, gluing, heat staking, clamping, buttoning, snapping a cover over an end, and/or snapping on an external part, (i) the imparted predetermined shape may direct pressure of the positioning and stabilising structure to predetermined portions of a wearers&#39; face, (j) the at least one rigidiser arm maybe incapable of stretching and is relatively more rigid than the at least one strap, (k) the positioning and stabilising structure may comprise two or more rigidiser arms symmetrically disposed on opposite sides of a patient&#39;s face, (l) the at least one rigidiser arm may be completely removable from the at least one strap, (m) the at least one strap may comprise two pockets, each receiving a rigidiser arm to releasably secure the at least one strap to the rigidiser arms, (n) the at least one strap may comprise at least one retaining means, said retaining means may comprise a loop, a sleeve and/or a pocket, for receiving the at least one rigidiser arm and holding the at least one rigidiser arm in place, (o) the at least one rigidiser arm may comprise at least one retaining means, said retaining means may comprise a loop, a sleeve and/or a pocket, for receiving the at least one strap and holding the at least one strap in place, (p) the at least one rigidiser arm may be affixed to a guiding element provided to the at least one strap, (q) the guiding element may be a loop- or sheath-like portion or passage or a pocket into which or through which the at least one rigidiser arm extends, (r) the guiding element may allow longitudinal expansion or retraction of the at least one strap relative to the at least one rigidiser arm and/or may allow substantially free movement or floating of the at least one rigidiser arm relative to the at least one strap, (s) said extension may be configured to allow flexing of the at least one rigidiser arm in a plane parallel with the patient&#39;s Frankfort horizontal, (t) said extension may be substantially equal in width to the main body, (u) the at least one strap may be substantially inelastic such that the positioning and stabilising structure is length-adjustable by at least one of flexing of the at least one rigidiser arm, ladder lock clips, buckle connections, and hook and loop connections, (v) a patient interface system for sealed delivery of a flow of breathable gas at a continuously positive pressure with respect to ambient air pressure to an entrance to the patient&#39;s airways including at least an entrance of a patient&#39;s nares, wherein the patient interface is configured to maintain a therapy pressure in a range of about 4 cmH2O to about 30 cmH2O, e.g., typically about 10 cmH2O, above ambient air pressure in use, throughout the patient&#39;s respiratory cycle, while the patient is sleeping, to ameliorate sleep disordered breathing, e.g., sleep apnea, the patient interface system may comprise: a positioning and stabilising structure according to any one or more of the above examples; and a patient interface comprising: a seal-forming structure to provide pressurized gas at least to both nares of the patient and a plenum chamber pressurised at a pressure above ambient pressure in use, the seal-forming structure and the plenum chamber formed in one piece, the plenum chamber including a plenum connection region, and the seal-forming structure is configured to seal around an inferior periphery of the patient&#39;s nose and below the bridge of the nose; a gas washout vent configured to allow a flow of patient exhaled CO2 to an exterior of the patient interface to minimise rebreathing of exhaled CO2 by the patient and a frame releasably attachable to the plenum connection region, (w) the extension may be permanently fixed to the mask frame and the main body is detachable from the extension, and/or (x) the extension and the main body may comprise one piece and the extension is detachable from the mask frame. 
     Another aspect of the present technology is directed to a cushion member for a patient interface for delivery of a supply of pressurised air or breathable gas to an entrance of a patient&#39;s airways. The cushion member may comprise: a retaining structure for repeatable engagement with and disengagement from a frame member; and a seal-forming structure having a nasal opening to provide pressurized gas to both nares of the patient and a plenum chamber formed in one piece, the seal-forming structure configured to seal around an inferior periphery of the patient&#39;s nose and below the bridge of the nose, and the seal-forming structure and plenum chamber permanently connected to the retaining structure; wherein the seal-forming structure is made from a first material and the retaining structure is made from a second material with different mechanical characteristics from the first material and the second material is more rigid than the first material; and wherein an increase in air pressure within the cushion member causes a sealing force between the seal-forming structure and the frame member to increase. 
     In examples, (a) the first material may be silicone and the second material may be silicone with a higher durometer than the first material, (b) the cushion member may comprise a plenum chamber located between the retaining structure and the seal-forming structure, (c) the cushion member may comprise a frame member made from the second material, (d) the first material may permit the seal-forming structure to readily conform to finger pressure and the second material may prevent the retaining structure from readily conforming to finger pressure, (e) said seal-forming structure may include a recessed portion to receive the tip of the nose of the patient, (f) a compliant region may be located above the recessed portion, said compliant region being thin and flexible relative to the remainder of the seal-forming structure, (g) said seal-forming structure may comprise foam, gel, and/or low durometer silicone, (h) said seal-forming structure may have a varied thickness around said nasal opening at predetermined positions, (i) said seal-forming structure may comprise a pair of protruding ends extending symmetrically about the nasal opening, each protruding end may be configured to seal against a region of the patient&#39;s face where the ala of the nose joins to the patient&#39;s face, (j) said seal-forming structure may comprise a pair of protruding end support sections corresponding to each protruding end and structured to support each protruding end and said pair of protruding end support sections may extend into a gas chamber defined at least in part by the seal-forming structure, (k) a lower portion of said seal-forming structure may be concave in a relaxed state to seal against the upper lip of the patient and to follow a curvature of the upper lip of the patient, (l) the seal-forming structure may comprise a dual wall cushion to prevent collapse of the seal-forming structure when the seal-forming structure is engaged with the nose of the patient to form a pneumatic seal, and/or (m) a patient interface for sealed delivery of a flow of breathable gas at a continuously positive pressure with respect to ambient air pressure to an entrance to the patient&#39;s airways including at least an entrance of a patient&#39;s nares, wherein the patient interface is configured to maintain a therapy pressure in a range of about 4 cmH2O to about 30 cmH2O above ambient air pressure in use, throughout the patient&#39;s respiratory cycle, while the patient is sleeping, to ameliorate sleep disordered breathing, said patient interface may comprise: the cushion member of any one of the above examples; a positioning and stabilising structure to maintain the cushion member in sealing contact with an area surrounding an entrance to at least the patient&#39;s nasal airways while maintaining a therapeutic pressure at the entrance to at least the patient&#39;s nasal airways; a plenum chamber pressurised at a pressure above ambient pressure in use; and a gas washout vent configured to allow a flow of patient exhaled CO2 to an exterior of the patient interface to minimise rebreathing of exhaled CO2 by the patient. 
     Another aspect of the present technology is directed to a patient interface to provide breathable gas to a patient. The patient interface may comprise: a seal-forming structure having a nasal opening to provide pressurized gas to both nares of the patient and a plenum chamber formed in one piece, the plenum chamber including a plenum connection region, and the seal-forming structure is configured to seal around an inferior periphery of the patient&#39;s nose and below the bridge of the nose; and a frame comprising a frame connection region and a headgear connection region; wherein the frame connection region is configured for attachment to the plenum chamber at the plenum connection region, and wherein a sealing lip is adapted to form a pneumatic seal between the plenum connection region and the frame connection region. 
     In examples, (a) the frame connection region may comprise at least one retention feature to facilitate connection with the plenum connection region, and the plenum connection region may comprise at least one complementary connection region to receive the at least one retention feature corresponding thereto, (b) the at least one retention feature may be a barb, said barb may have a leading surface and a trailing surface and the at least one complementary connection region may comprise a lead-in surface and a retaining surface, (c) said seal-forming structure may include a recessed portion to receive the tip of the nose of the patient, (d) a compliant region may be located above the recessed portion, said compliant region being thin and flexible relative to the remainder of the seal-forming structure, (e) said seal-forming structure may comprise foam, gel, and/or low durometer silicone, (f) said seal-forming structure may have a varied thickness around said nasal opening at predetermined positions, (g) said seal-forming structure may comprise a pair of protruding ends extending symmetrically about the nasal opening, each protruding end may be configured to seal against a region of the patient&#39;s face where the ala of the nose joins to the patient&#39;s face, (h) said seal-forming structure may comprise a pair of protruding end support sections corresponding to each protruding end and structured to support each protruding end and said pair of protruding end support sections may extend into a gas chamber defined at least in part by the seal-forming structure, (i) a lower portion of said seal-forming structure may be concave in a relaxed state to seal against the upper lip of the patient and to follow a curvature of the upper lip of the patient, and/or (j) the seal-forming structure may comprise a dual wall cushion to prevent collapse of the seal-forming structure when the seal-forming structure is engaged with the nose of the patient to form a pneumatic seal. 
     Another aspect of the present technology is directed to a cushion member for a nasal cradle mask for delivery of a supply of pressurised air or breathable gas to an entrance of a patient&#39;s airways. The cushion member may comprise: a retaining structure for repeatable engagement with and disengagement from a frame member; and a seal-forming structure having a nasal opening to provide pressurized gas to both nares of the patient and a plenum chamber formed in one piece, the seal-forming structure configured to seal around an inferior periphery of the patient&#39;s nose and below the bridge of the nose, and the seal-forming structure and plenum chamber permanently connected to the retaining structure; wherein an increase in air pressure within the cushion member causes a sealing force between the seal-forming structure and the frame member to increase; and wherein a retention force between the retaining structure and the frame member is higher than a disengagement force to disengage the retaining structure from the frame member. 
     In examples, (a) said seal-forming structure may include a recessed portion to receive the tip of the nose of the patient, (b) a compliant region may be located above the recessed portion, said compliant region being thin and flexible relative to the remainder of the seal-forming structure, (c) said seal-forming structure may comprise foam, gel, and/or low durometer silicone, (d) said seal-forming structure may have a varied thickness around said nasal opening at predetermined positions, (e) said seal-forming structure may comprise a pair of protruding ends extending symmetrically about the nasal opening, each protruding end may be configured to seal against a region of the patient&#39;s face where the ala of the nose joins to the patient&#39;s face, (f) said seal-forming structure may comprise a pair of protruding end support sections corresponding to each protruding end and structured to support each protruding end and said pair of protruding end support sections may extend into a gas chamber defined at least in part by the seal-forming structure, (g) a lower portion of said seal-forming structure may be concave in a relaxed state to seal against the upper lip of the patient and to follow a curvature of the upper lip of the patient, (h) the seal-forming structure may comprise a dual wall cushion to prevent collapse of the seal-forming structure when the seal-forming structure is engaged with the nose of the patient to form a pneumatic seal, and/or (i) a patient interface for sealed delivery of a flow of breathable gas at a continuously positive pressure with respect to ambient air pressure to an entrance to the patient&#39;s airways including at least an entrance of a patient&#39;s nares, wherein the patient interface is configured to maintain a therapy pressure in a range of about 4 cmH2O to about 30 cmH2O above ambient air pressure in use, throughout the patient&#39;s respiratory cycle, while the patient is sleeping, to ameliorate sleep disordered breathing, said patient interface may comprise: the cushion member of any one of the above examples; a positioning and stabilising structure to maintain the cushion member in sealing contact with an area surrounding an entrance to at least the patient&#39;s nasal airways while maintaining a therapeutic pressure at the entrance to at least the patient&#39;s nasal airways; a plenum chamber pressurised at a pressure above ambient pressure in use; and a gas washout vent configured to allow a flow of patient exhaled CO2 to an exterior of the patient interface to minimise rebreathing of exhaled CO2 by the patient. 
     Another aspect of the present technology is directed to a cushion member for a patient interface for delivery of a supply of pressurised air or breathable gas to an entrance of a patient&#39;s airways. The cushion member may comprise: a retaining structure for repeatable engagement with and disengagement from a frame member; and a seal-forming structure having a nasal opening to provide pressurized gas to both nares of the patient and a plenum chamber formed in one piece, the seal-forming structure configured to seal around an inferior periphery of the patient&#39;s nose and below the bridge of the nose, and the seal-forming structure and plenum chamber permanently connected to the retaining structure, wherein said seal-forming structure includes a recessed portion to receive the tip of the nose of the patient, and wherein said seal-forming structure comprises a pair of protruding ends extending symmetrically about the nasal opening, each protruding end configured to seal against a region of the patient&#39;s face where the ala of the nose joins to the patient&#39;s face. 
     In examples, (a) the seal-forming structure may comprise a dual wall cushion to prevent collapse of the seal-forming structure when the seal-forming structure is engaged with the nose of the patient to form a pneumatic seal, (b) a compliant region may be located above the recessed portion, said compliant region being thin and flexible relative to the remainder of the seal-forming structure, (c) said seal-forming structure may comprise foam, gel, and/or low durometer silicone, (d) said seal-forming structure may have a varied thickness around said nasal opening at predetermined positions, (e) the seal-forming structure may include an overhang at the nasal opening of the seal-forming structure, said overhang located proximal to the recessed portion, (d) said seal-forming structure may comprise a pair of protruding end support sections corresponding to each protruding end and structured to support each protruding end and said pair of protruding end support sections may extend into a gas chamber defined at least in part by the seal-forming structure, (e) a lower portion of said seal-forming structure may be concave in a relaxed state to seal against the upper lip of the patient and to follow a curvature of the upper lip of the patient, (f) said lower portion may have a reduced material thickness relative to the rest of the seal-forming structure, and/or (g) a patient interface for sealed delivery of a flow of breathable gas at a continuously positive pressure with respect to ambient air pressure to an entrance to the patient&#39;s airways including at least an entrance of a patient&#39;s nares, wherein the patient interface is configured to maintain a therapy pressure in a range of about 4 cmH2O to about 30 cmH2O above ambient air pressure in use, throughout the patient&#39;s respiratory cycle, while the patient is sleeping, to ameliorate sleep disordered breathing, said patient interface may comprise: the cushion member of any one of the above examples; a positioning and stabilising structure to maintain the cushion member in sealing contact with an area surrounding an entrance to at least the patient&#39;s nasal airways while maintaining a therapeutic pressure at the entrance to at least the patient&#39;s nasal airways; a plenum chamber pressurised at a pressure above ambient pressure in use; and a gas washout vent configured to allow a flow of patient exhaled CO2 to an exterior of the patient interface to minimise rebreathing of exhaled CO2 by the patient. 
     Another aspect of the present technology is directed to a patient interface system to provide breathable gas to a patient. The patient interface may comprise: a patient interface including a seal-forming structure to provide a pneumatic connection to a patient&#39;s airways; and a positioning and stabilising structure including at least one strap and at least one rigidiser arm and configured to releasably retain the patient interface on the patient, wherein the at least one strap may be permanently attached to the at least one rigidiser arm at an attachment point. 
     In examples, (a) the attachment point may comprise an ultrasonic weld, (b) the attachment point may comprise a heat stake, (c) the attachment point may comprise stitching, (d) the attachment point may comprise a hinged mechanism, and/or (e) the attachment point may comprise barbs on the at least one rigidiser arm. 
     Another aspect of the present technology is directed to a patient interface system to provide breathable gas to a patient. The patient interface may comprise: a patient interface including a seal-forming structure to provide a pneumatic connection to a patient&#39;s airways; and a positioning and stabilising structure including at least one strap and at least one rigidiser arm and configured to releasably retain the patient interface on the patient, wherein the at least one strap may be releasably attached to the at least one rigidiser arm. 
     In examples, (a) the at least one strap may comprise an elastic tube and the at least one rigidiser arm may comprise a raised stop, (b) the at least rigidiser arm may comprise a tab to releasably attach the at least one strap with a hook and loop connection, (c) the at least one strap may comprise at least one lock and the at least one rigidiser arm may comprise at least one notch that corresponds with said at least one lock, and/or (d) the at least one strap may comprise an end having hook material to form a hook and loop connection with a loop material on the at least one strap by looping the at least one strap through a first slot and a second slot of the at least one rigidiser arm. 
     Another aspect of the present technology is directed to a patient interface system to provide breathable gas to a patient. The patient interface may comprise: a patient interface including a seal-forming structure to provide a pneumatic connection to a patient&#39;s airways; and a positioning and stabilising structure including at least one strap and at least one rigidiser arm and configured to releasably retain the patient interface on the patient, wherein the at least one rigidiser arm may be releasably attachable to a frame of the patient interface, the frame supporting the seal-forming structure against the patient&#39;s face. 
     In examples, (a) the at least one rigidiser arm may be releasably attachable to a corresponding extension of the frame in a rotate and lock arrangement, (b) the patient interface may further comprise pins and corresponding sockets to releasably attach the at least one rigidiser arm to an extension of the frame, (c) the at least one rigidiser may further comprise a projection and an arm supported on a shaft to releasably attach the at least one rigidiser arm to an extension of the frame at a shaft receiver and an arm receiver, (d) the at least one rigidiser arm may comprise an extension to releasably attach to a receiver of the frame with a snap-fit, (e) the at least one rigidiser arm may comprise an extension to releasably attach to a receiver of the frame with a press-fit, (f) the at least one rigidiser arm may comprise an extension having a column to releasably attach to a receiver of the frame with a snap-fit, the extension may further comprise an end to prevent rotation about a longitudinal axis of the column, (g) the frame may comprise at least one slot through which a corresponding at least one rigidiser arm may be threaded for releasable attachment, the at least one rigidiser arm may comprise a locking end, (h) the at least one rigidiser arm may comprise an extension with a pin to releasably attach to a socket of the frame with a snap-fit, (i) the at least one rigidiser arm may comprise a first magnet and the frame may comprise a second magnet to releasably attach the at least one rigidiser arm to the frame, (j) the at least one rigidiser arm may comprise a first L-shaped section having at least one post and the frame may comprise a second L-shaped section having at least one hole and the at least one rigidiser arm may be releasably attached to the frame by engagement between the at least one post and the at least one hole, (k) the frame may comprise a boss and the at least one rigidiser arm may comprise a cavity to releasably attach to said boss, and/or (l) the at least one rigidiser arm may comprise prongs and a hole and an extension of the frame may comprise slots corresponding with said prongs and a post corresponding with said hole for releasable attachment between the at least one rigidiser arm and the frame. 
     Another aspect of the present technology is directed to a patient interface system to provide breathable gas to a patient. The patient interface may comprise: a patient interface including a seal-forming structure to provide a pneumatic connection to a patient&#39;s airways; and a positioning and stabilising structure including at least one strap and at least one rigidiser arm and configured to releasably retain the patient interface on the patient, wherein an extension joins each at least one rigidiser arm to a frame of the patient interface, the frame supporting the seal-forming structure against the patient&#39;s face. 
     In examples, (a) the at least one rigidiser arm may comprise ribs at a bend to resist deformation at the bend, (b) the extension may comprise ribs at a bend to resist deformation at the bend, and/or (c) the extension may comprise a longitudinal rib along a bend and straight section of the extension to resist deformation. 
     Another aspect of the present technology is directed to a patient interface for sealed delivery of a flow of breathable gas at a continuously positive pressure with respect to ambient air pressure to an entrance to the patient&#39;s airways including at least an entrance of a patient&#39;s nares, wherein the patient interface is configured to maintain a therapy pressure in a range of about 4 cmH2O to about 30 cmH2O, e.g., typically about 10 cmH2O, above ambient air pressure in use, throughout the patient&#39;s respiratory cycle, while the patient is sleeping, to ameliorate sleep disordered breathing, e.g., sleep apnea, said patient interface may comprise: a sealing structure to form seal with at least nasal airways of the patient; a positioning and stabilising structure to maintain the sealing structure in sealing contact with an area surrounding an entrance to at least the patient&#39;s nasal airways while maintaining a therapeutic pressure at the entrance to at least the patient&#39;s nasal airways; a plenum chamber pressurised at a pressure above ambient pressure in use; a gas washout vent configured to allow a flow of patient exhaled CO2 to an exterior of the patient interface to minimise rebreathing of exhaled CO2 by the patient. 
     Of course, portions of the aspects may form sub-aspects of the present technology. Also, various ones of the, examples, sub-aspects and/or aspects may be combined in various manners and also constitute additional aspects or sub-aspects of the present technology. 
     Other features of the technology will be apparent from consideration of the information contained in the following detailed description, abstract, drawings and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The present technology is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings, in which like reference numerals refer to similar elements including: 
       Treatment Systems 
         FIG.  1   a    shows a system in accordance with the present technology. A patient  1000  wearing a patient interface  3000 , receives a supply of air at positive pressure from a PAP device  4000 . Air from the PAP device  4000  is humidified in a humidifier  5000 , and passes along an air circuit  4170  to the patient  1000 . 
         FIG.  1   b    shows a PAP device  4000  in use on a patient  1000  with a nasal mask. 
         FIG.  1   c    shows a PAP device  4000  in use on a patient  1000  with a full-face mask. 
       Therapy 
       Respiratory System 
         FIG.  2   a    shows an overview of a human respiratory system including the nasal and oral cavities, the larynx, vocal folds, oesophagus, trachea, bronchus, lung, alveolar sacs, heart and diaphragm. 
         FIG.  2   b    shows a view of a human upper airway including the nasal cavity, nasal bone, lateral nasal cartilage, greater alar cartilage, nostril, lip superior, lip inferior, larynx, hard palate, soft palate, oropharynx, tongue, epiglottis, vocal folds, oesophagus and trachea. 
       Facial Anatomy 
         FIG.  2   c    is a front view of a face with several features of surface anatomy identified including the lip superior, upper vermillion, lower vermillion, lip inferior, mouth width, endocanthion, a nasal ala, nasolabial sulcus and cheilion. 
         FIG.  2   d    is a side view of a head with several features of surface anatomy identified including glabella, sellion, pronasale, subnasale, lip superior, lip inferior, supramenton, nasal ridge, otobasion superior and otobasion inferior. Also indicated are the directions superior &amp; inferior, and anterior &amp; posterior. 
         FIG.  2   e    is a further side view of a head. The approximate locations of the Frankfort horizontal and nasolabial angle are indicated. 
         FIG.  2   f    shows a base view of a nose. 
         FIG.  2   g    shows a side view of the superficial features of a nose. 
         FIG.  2   h    shows subcutaneal structures of the nose, including lateral cartilage, septum cartilage, greater alar cartilage, lesser alar cartilage and fibrofatty tissue. 
         FIG.  2   i    shows a medial dissection of a nose, approximately several millimeters from a sagittal plane, amongst other things showing the septum cartilage and medial crus of greater alar cartilage. 
         FIG.  2   j    shows a front view of the bones of a skull including the frontal, temporal, nasal and zygomatic bones. Nasal concha are indicated, as are the maxilla, mandible and mental protuberance. 
         FIG.  2   k    shows a lateral view of a skull with the outline of the surface of a head, as well as several muscles. The following bones are shown: frontal, sphenoid, nasal, zygomatic, maxilla, mandible, parietal, temporal and occipital. The mental protuberance is indicated. The following muscles are shown: digastricus, masseter sternocleidomastoid and trapezius. 
         FIG.  2   l    shows an anterolateral view of a nose. 
       Pap Device and Humidifier 
         FIG.  3   a    shows an exploded view of a PAP device according to an example of the present technology. 
         FIG.  3   b    shows a perspective view of a humidifier in accordance with one form of the present technology. 
         FIG.  3   c    shows a schematic diagram of the pneumatic circuit of a PAP device in accordance with one form of the present technology. The directions of upstream and downstream are indicated. 
       Patient Interface 
         FIG.  4    is an anterior view of a plenum chamber in accordance with one form of the present technology. 
         FIG.  5    is a cross section along line  5 - 5  of  FIG.  4   . 
         FIG.  6    is an enlarged detail view taken from  FIG.  5   . 
         FIG.  7    is a perspective view from the top of the plenum chamber shown in  FIG.  4   . 
         FIG.  8    is a cross-section along line  8 - 8  of  FIG.  7   . 
         FIG.  9    is an enlarged detail view taken from  FIG.  8   . 
         FIG.  10    is a perspective view from the front side of a plenum chamber according to one example of the present technology. 
         FIG.  11    is a view of the plenum chamber shown in  FIG.  4   . 
         FIG.  12    is a cross-section taken along line  12 - 12  of  FIG.  11   . 
         FIG.  13    is an enlarged detail view taken from  FIG.  12   . 
         FIG.  14    is an enlarged cross-sectional view of the plenum connection region. 
         FIG.  15    is a side view of the patient interface shown in  FIG.  11   . 
         FIG.  16    is a cross-section taken along line  16 - 16  of  FIG.  15   . 
         FIG.  17    is an enlarged detail view taken from  FIG.  16   . 
         FIG.  18    is a side view of a patient interface in position on a model patient&#39;s head without any positioning and stabilising structure shown. 
         FIG.  19    is a partial, inferior view of a portion of a patient interface in position on a model patient&#39;s head accordance with one form of the present technology. Note that only a portion of the positioning and stabilising structure connecting to the frame is shown for clarity. 
         FIG.  20    is a side view of a plenum connection region of a plenum chamber in accordance with one form of the present technology. 
         FIG.  21    is a view of a superior portion thereof. 
         FIG.  22    is an anterior view thereof. 
         FIG.  23    is an inferior view thereof. 
         FIG.  24    is a perspective view thereof. 
         FIG.  25    is a cross-sectional view of the connection portion and the frame connection region, wherein the plenum chamber and the frame are not engaged. 
         FIG.  26    is a cross-sectional view of the connection portion and the frame connection region, wherein the plenum chamber and the frame are in contact but not fully engaged. 
         FIG.  27    is a cross-sectional view of the connection portion and the frame connection region, wherein the plenum chamber and the frame are nearly in full engagement with another such that the retention feature is deflected. 
         FIG.  28    is a cross-sectional view of the connection portion and the frame connection region, wherein the plenum chamber and the frame are engaged but separated such that the retention feature is deflected. 
         FIG.  29    is a cross-sectional view of the connection portion and the frame connection region, wherein the plenum chamber and the frame are fully engaged. 
         FIG.  30    is a rear perspective view of a patient interface according to an example of the present technology with the plenum chamber and seal-forming structure detached. 
         FIG.  31    is a front perspective view of a patient interface according to an example of the present technology with the plenum chamber and seal-forming structure detached. 
         FIG.  32    is a rear view of a patient interface according to an example of the present technology with the plenum chamber and seal-forming structure detached. 
         FIG.  33    is a side view of a patient interface according to an example of the present technology with the plenum chamber and seal-forming structure detached. 
         FIG.  34    shows a perspective view of a patient interface according to another example of the present technology indicating the attachment of an exemplary seal-forming structure and plenum chamber to a frame of the patient interface. 
         FIG.  35    shows a cross-sectional view of a patient interface including a mask frame, a flexible joint, and a rigidiser arm according to an example of the present technology. 
         FIG.  36    shows a perspective view of a patient interface including a mask frame, a flexible joint, and a rigidiser arm according to an example of the present technology. 
         FIG.  37    shows an exploded view of a patient interface including a mask frame, a flexible joint, and a rigidiser arm according to an example of the present technology. 
         FIG.  38    shows a detailed view of an end of a rigidiser arm according to an example of the present technology. 
         FIG.  39    shows a perspective view of a patient interface including a mask frame, flexible joints, and rigidiser arms according to an example of the present technology. 
         FIG.  40    shows a cross-sectional view of a patient interface including a mask frame, flexible joints, and rigidiser arms according to an example of the present technology. 
         FIG.  41    shows a perspective view of a rigidiser arm according to an example of the present technology. 
         FIG.  42    shows a cross-sectional view of a patient interface including a mask frame, a flexible joint, and a rigidiser arm according to an example of the present technology. 
         FIG.  43    shows a perspective view of a patient interface including a mask frame, a flexible joint, and a rigidiser arm according to an example of the present technology. 
         FIG.  44    shows an exploded view of a patient interface including a mask frame, a flexible joint, and a rigidiser arm according to an example of the present technology. 
         FIG.  45    shows a detailed view of an end of a rigidiser arm according to an example of the present technology. 
         FIG.  46    shows a detailed view of an end of a rigidiser arm and a flexible joint according to an example of the present technology. 
         FIG.  47    shows a cross-sectional view of a rigidiser and a mask frame according to an example of the present technology. 
         FIG.  48    shows a detailed cross-sectional view of a rigidiser arm and mask frame according to an example of the present technology. 
         FIG.  49    shows a cross-sectional view of rigidiser arms and a mask frame according to an example of the present technology. 
         FIG.  50    shows a perspective view of rigidiser arms and a mask frame according to an example of the present technology. 
         FIG.  51    shows a detailed perspective view of the connection between a rigidiser and a mask frame according to an example of the present technology. 
         FIG.  52    shows a top view of rigidiser arms and a mask frame according to an example of the present technology, and in broken line indicates flexing of the rigidiser arm in a laterally outwards direction in the coronal plane. 
         FIG.  53    shows a detailed top view of the connection between a rigidiser and a mask frame according to an example of the present technology. 
         FIG.  54    shows a cross-sectional perspective view of rigidiser arms and a mask frame according to an example of the present technology. 
         FIG.  55    shows a side view of a rigidiser and a mask frame according to an example of the present technology, and in broken line indicates flexing of the rigidiser arm in a vertically downward direction in the sagittal plane. 
         FIG.  56    shows a front view of a rigidiser and a mask frame according to an example of the present technology. 
         FIG.  57    shows a perspective view of rigidiser arms and a mask frame according to an example of the present technology. 
         FIG.  58    shows a partially exploded perspective view of rigidiser arms and a mask frame according to an example of the present technology. 
         FIG.  59    shows a detailed and partially exploded perspective view of a rigidiser and a mask frame according to an example of the present technology. 
         FIG.  60    shows a perspective view of a rigidiser according to an example of the present technology. 
         FIG.  61    shows a view of a rigidiser arm according to an example of the present technology plotted on a grid in an X-Y plane. 
         FIG.  62    shows a view of a rigidiser arm according to an example of the present technology plotted on a grid in an X-Z plane. 
         FIG.  63    shows a view of a rigidiser arm according to an example of the present technology plotted on a grid in a Y-Z plane. 
         FIG.  64    shows a view of a rigidiser arm according to an example of the present technology plotted in three dimensions. 
         FIG.  65    shows a schematic perspective view of a positioning and stabilising structure in accordance with an example of the present technology. 
         FIG.  66    shows a cross-sectional view of a positioning and stabilising structure taken along line  66 - 66  in  FIG.  65   . 
         FIG.  67    shows a schematic side view of an exemplary rigidiser arm for a positioning and stabilising structure in accordance with the present technology. 
         FIG.  68    shows a schematic perspective view of an exemplary positioning and stabilising structure containing a rigidiser arm in accordance with the present technology in a first state. 
         FIG.  69    shows a schematic perspective view of an exemplary positioning and stabilising structure containing a rigidiser arm in accordance with the present technology in a second state. 
         FIG.  70    shows a schematic perspective view of an exemplary positioning and stabilising structure containing a rigidiser arm in accordance with the present technology in a third state. 
         FIG.  71    shows a perspective view of an exemplary positioning and stabilising structure in accordance with the present technology donned on a patient. 
         FIG.  72    shows a front view of an exemplary positioning and stabilising structure in accordance with the present technology donned on a patient. 
         FIG.  73    shows a side view of an exemplary positioning and stabilising structure in accordance with the present technology donned on a patient. 
         FIG.  74    shows a perspective view of an exemplary positioning and stabilising structure in accordance with the present technology donned on a patient. 
         FIG.  75    shows a front view of an exemplary positioning and stabilising structure in accordance with the present technology donned on a patient. 
         FIG.  76    shows a side view of an exemplary positioning and stabilising structure in accordance with the present technology donned on a patient. 
         FIG.  77    shows a downward perspective view of an exemplary positioning and stabilising structure in accordance with the present technology donned on a patient. 
         FIG.  78    shows a graph of the extension (in mm) of a strap of a positioning and stabilising structure according to an example of the present technology subjected to a range of loads (in Newtons). 
         FIG.  79    shows a top view of a strap of a positioning and stabilising structure according to an example of the present technology during an intermediate stage of production. 
         FIG.  80    shows a cross-sectional view taken through line  80 - 80  of  FIG.  79    of a strap of a positioning and stabilising structure according to an example of the present technology during an intermediate stage of production. 
         FIG.  81    shows a top view of a strap of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  82    shows a top detailed view of a strap of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  83    shows a cross-sectional view taken through line  83 - 83  of  FIG.  81    of a strap of a positioning and stabilising structure according to an example of the present technology. 
         FIGS.  84  to  88    show a sequence of perspective views of a patient donning a positioning and stabilising structure according to an example of the present technology. 
         FIGS.  89  to  93    show a sequence of side views of a patient donning a positioning and stabilising structure according to an example of the present technology. 
         FIGS.  94  to  98    show a sequence of front views of a patient donning a positioning and stabilising structure according to an example of the present technology. 
         FIGS.  99  to  104    show a sequence of side views of a patient donning a positioning and stabilising structure according to an example of the present technology. 
         FIGS.  105  to  107    show a sequence of perspective views of a patient adjusting a patient interface according to an example of the present technology. 
         FIGS.  108  to  112    show a sequence of rear views of a patient adjusting a positioning and stabilising structure according to an example of the present technology. 
         FIG.  113    shows a detailed view of the connection between a strap and a rigidiser arm of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  114    shows another detailed view of the connection between a strap and a rigidiser arm of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  115    shows another detailed view of the connection between a strap and a rigidiser arm of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  116    shows another detailed view of the connection between a strap and a rigidiser arm of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  117    shows another detailed view of the connection between a strap and a rigidiser arm of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  118    shows another detailed view of the connection between a strap and a rigidiser arm of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  119    shows a detailed view of the connection between a strap and a rigidiser arm of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  120    shows another detailed view of the connection between a strap and a rigidiser arm of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  121    shows another detailed view of the connection between a strap and a rigidiser arm of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  122    shows another detailed view of the connection between a strap and a rigidiser arm of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  123    shows a detailed view of a split region of a strap of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  124    shows another detailed view of a split region of a strap of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  125    shows another detailed view of a split region of a strap of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  126    shows a detailed view of a bifurcation of a strap of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  127    shows another detailed view of a bifurcation of a strap of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  128    shows another detailed view of a bifurcation of a strap of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  129    shows another detailed view of a bifurcation of a strap of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  130    shows another detailed view of a bifurcation of a strap of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  131    shows another detailed view of a bifurcation of a strap of a positioning and stabilising structure according to an example of the present technology. 
         FIG.  132    shows a perspective view of a positioning and stabilising structure manufactured according to an example of the present technology. 
         FIG.  133    shows a process of forming a positioning and stabilising structure straps from a continuous roll according to an example of the present technology. 
         FIG.  134    shows a conventional example depicting a knitting process according to an example of the present technology. 
         FIG.  135    shows a conventional example depicting a knitting process according to an example of the present technology. 
         FIG.  136    illustrates a basic warp knitted fabric according to an example of the present technology. 
         FIG.  137    is a schematic representation of the basic warp knitted fabric of  FIG.  136   . 
         FIG.  138    illustrates a basic warp knitted fabric according to an example of the present technology. 
         FIG.  139    illustrates a basic weft knitted fabric according to an example of the present technology. 
         FIG.  140    is a side view of a positioning and stabilising structure positioned on a patient&#39;s head in accordance with an example of the present technology. 
         FIG.  141    shows the changing direction of the course or grain of the positioning and stabilising structure of  FIG.  140    according to an example of the present technology. 
         FIG.  142    illustrates an increased stretch in the direction of the course of a knitted positioning and stabilising structure according to an example of the present technology. 
         FIG.  143    shows 3D printed links used to form a positioning and stabilising structure according to an example of the present technology 
         FIG.  144    shows a 3D printed positioning and stabilising structure piece including a rigidiser according to an example of the present technology. 
         FIG.  145    shows a 3D printed positioning and stabilising structure straps and clips according to an example of the present technology. 
         FIG.  146    shows a rear perspective view of a vent for a patient interface in accordance with one form of the present technology. 
         FIG.  147    shows a front perspective view of a vent for a patient interface in accordance with one form of the present technology. 
         FIG.  148    shows a rear perspective view of a vent for a patient interface in accordance with one form of the present technology. 
         FIG.  149    shows a side perspective view of a vent for a patient interface in accordance with one form of the present technology. 
         FIG.  150    shows a side perspective view of a vent for a patient interface in accordance with one form of the present technology. 
         FIG.  151    shows a side perspective view of a vent for a patient interface in accordance with one form of the present technology. 
         FIG.  152    shows a top perspective view of a vent for a patient interface in accordance with one form of the present technology. 
         FIG.  153    is a process flow diagram depicting a method for manufacturing a patient interface for the treatment of respiratory disorders in accordance with an example of the present technology. 
         FIG.  154    is a system diagram generally depicting equipment used for carrying out the method of  FIG.  153   . 
         FIG.  155    is a top view of a textile depicting vent portions after heat staking in accordance with an example of the present technology. 
         FIG.  156    is a magnified top view of a peripheral edge of a vent portion before heat staking in accordance with an example of the present technology. 
         FIG.  157    is a magnified top view of a peripheral edge of a vent portion after heat staking in accordance with an example of the present technology. 
         FIG.  158    is a magnified sectional side view of a peripheral edge of a vent portion before heat staking in accordance with an example of the present technology. 
         FIG.  159    is a magnified sectional side view of a peripheral edge of a vent portion after heat staking in accordance with an example of the present technology. 
         FIG.  160    shows a short tube in a neutral state according to an example of the present technology. 
         FIG.  161    shows a side view of a short tube in a compressed state according to an example of the present technology. 
         FIG.  162    shows a side view of a short tube in an elongated state according to an example of the present technology. 
         FIG.  163    shows a side view of a short tube in a curved state according to an example of the present technology. 
         FIG.  164    shows a cross-sectional view of a short tube taken along line  163 - 163  as shown in  FIG.  163    according to an example of the present technology. 
         FIG.  165    shows a perspective view of a short tube in a curved and elongated state according to an example of the present technology. 
         FIG.  166    is a perspective view showing a patient interface system in accordance with one form of the present technology in use on a patient. 
         FIG.  167    is a chart depicting vertical plane air speed in m/s along the x and z axes from a vent of a SWIFT FX™ nasal pillows mask by ResMed Limited. 
         FIG.  168    is a chart depicting horizontal plane air speed in m/s along the x and y axes from a vent of a SWIFT FX™ nasal pillows mask by ResMed Limited. 
         FIG.  169    is a chart depicting vertical plane signal along the x and y axes from a vent of a SWIFT FX™ nasal pillows mask by ResMed Limited. 
         FIG.  170    is a chart depicting horizontal plane signal along the x and y axes from a vent of a SWIFT FX™ nasal pillows mask by ResMed Limited. 
         FIG.  171    is a chart depicting vertical plane air speed in m/s along the x and z axes from a vent of a patient interface system in accordance with one form of the present technology. 
         FIG.  172    is a chart depicting horizontal plane air speed in m/s along the x and y axes from a vent of a patient interface system in accordance with one form of the present technology. 
         FIG.  173    is a chart depicting vertical plane signal along the x and y axes from a vent of a patient interface system in accordance with one form of the present technology. 
         FIG.  174    is a chart depicting horizontal plane signal along the x and y axes from a vent of a patient interface system in accordance with one form of the present technology. 
         FIG.  175    is a chart comparing velocity (in m/s) along a vent axis according to distance (in mm) from a vent of a SWIFT FX™ nasal pillows mask by ResMed Limited and a vent of a patient interface system in accordance with one form of the present technology. 
         FIG.  176    is a bottom perspective view of a reinforcement portion folded over the end of a strap of a positioning and stabilising structure in accordance with one form of the present technology 
         FIG.  177    is a top planar view of a reinforcement portion folded over the end of a strap of a positioning and stabilising structure in accordance with one form of the present technology. 
         FIG.  178    is a side perspective view of a reinforcement portion folded over the end of a strap of a positioning and stabilising structure in accordance with one form of the present technology. 
         FIG.  179    is a side planar view of a reinforcement portion folded over the end of a strap of a positioning and stabilising structure in accordance with one form of the present technology. 
         FIG.  180    is a magnified view of  FIG.  179   . 
         FIG.  181    is a magnified view of  FIG.  177   . 
         FIGS.  182  to  184    show a series of steps of removing a strap from a rigidiser arm of a positioning and stabilising structure in accordance with one form of the present technology. 
         FIGS.  185  and  186    show a series of steps of attaching a strap to a rigidiser arm of a positioning and stabilising structure in accordance with one form of the present technology. 
         FIG.  187    is a side planar view of a rigidiser arm of a positioning and stabilising structure in accordance with one form of the present technology showing a visual indicator. 
         FIG.  188    is a side planar view of a rigidiser arm of a positioning and stabilising structure in accordance with one form of the present technology showing a visual indicator. 
         FIG.  189    is a front planar view of fame and rigidiser arms in accordance with one form of the present technology showing visual and tactile indicators. 
         FIG.  190    is a top planar view of a seal-forming structure in accordance with one form of the present technology showing a visual indicator. 
         FIG.  191    is a rear planar view of a seal-forming structure in accordance with one form of the present technology showing a visual indicator. 
         FIG.  192    is a top perspective view of a seal-forming structure in accordance with one form of the present technology showing a visual indicator. 
         FIG.  193    is a cross-sectional view taken through line  193 - 193  of  FIG.  192   . 
         FIG.  194    is a cross-sectional view taken through line  194 - 194  of  FIG.  192   . 
         FIG.  195    is a rear planar view of a frame in accordance with one form of the present technology. 
         FIG.  196    is a top planar view of a frame in accordance with one form of the present technology. 
         FIG.  197    is a rear perspective view of a frame in accordance with one form of the present technology. 
         FIG.  198    is a side planar view of a frame in accordance with one form of the present technology. 
         FIG.  199    is a rear planar view of a retaining structure of a plenum connection region in accordance with one form of the present technology. 
         FIG.  200    is a bottom planar view of a retaining structure of a plenum connection region in accordance with one form of the present technology. 
         FIG.  201    is a rear perspective view of a retaining structure of a plenum connection region in accordance with one form of the present technology. 
         FIG.  202    is a side planar view of a retaining structure of a plenum connection region in accordance with one form of the present technology. 
         FIGS.  203  to  207    show a tube in accordance with one form of the present technology being elongated by a distance of 30 mm, 60 mm, 90 mm, and 120 mm with a lower end of the tube held in a fixed position with its longitudinal axis at its lower end being perpendicular to the direction of elongation before elongation commences. 
         FIGS.  208  to  212    show a ResMed™ Swift FX™ Nasal Pillows Mask tube being elongated by a distance of 30 mm, 60 mm, 90 mm, and 120 mm with a lower end of the tube held in a fixed position with its longitudinal axis at its lower end being perpendicular to the direction of elongation before elongation commences. 
         FIGS.  213  to  217    show a Philips™ Respironics™ GoLife™ Nasal Pillows Mask tube being elongated by a distance of 30 mm, 60 mm, 90 mm, and 120 mm with a lower end of the tube is held a fixed position with its longitudinal axis at its lower end being perpendicular to the direction of elongation before elongation commences. 
         FIGS.  218  to  222    show a Philips™ Respironics™ Wisp™ Nasal Mask tube being elongated by a distance of 30 mm, 60 mm, 90 mm, and 120 mm with a lower end of the tube held in a fixed position with its longitudinal axis at its lower end being perpendicular to the direction of elongation before elongation commences. 
         FIG.  223    shows a front view of a patient interface system according to an example of the present technology. 
         FIG.  224    shows a top view of a patient interface system according to an example of the present technology. 
         FIG.  225    shows a left side view of a patient interface system according to an example of the present technology. 
         FIG.  226    shows a right side view of a patient interface system according to an example of the present technology. 
         FIG.  227    shows another left side view of a patient interface system according to an example of the present technology. 
         FIG.  228    shows another top view of a patient interface system according to an example of the present technology. 
         FIG.  229    shows another top view of a patient interface system according to an example of the present technology. 
         FIG.  230    shows a rear view of a patient interface system according to an example of the present technology. 
         FIG.  231    shows another rear view of a patient interface system according to an example of the present technology. 
         FIG.  232    shows a rear perspective view of a patient interface system according to an example of the present technology. 
         FIG.  233   a    shows a front view of a patient interface system according to an example of the present technology worn by a patient. 
         FIG.  233   b    shows a top view of a patient interface system according to an example of the present technology worn by a patient. 
         FIG.  233   c    shows a left side view of a patient interface system according to an example of the present technology worn by a patient. 
         FIG.  233   d    shows a front perspective view of a patient interface system according to an example of the present technology worn by a patient. 
         FIG.  233   e    shows a right side perspective view of a patient interface system according to an example of the present technology worn by a patient. 
         FIG.  233   f    shows a detailed right side perspective view of a patient interface system according to an example of the present technology worn by a patient. 
         FIG.  233   g    shows another right side perspective view of a patient interface system according to an example of the present technology worn by a patient. 
         FIG.  233   h    shows a top view of a patient interface system according to an example of the present technology worn by a patient. 
         FIG.  234   a    shows a top view of a nasal cradle cushion of a patient interface in accordance with an example of the present technology. 
         FIG.  234   b    shows a bottom cross-sectional view taken through line  234   c - 234   c  of  FIG.  234   a    of a nasal cradle cushion of a patient interface in accordance with an example of the present technology. 
         FIG.  234   c    shows a side cross-sectional view taken through line  234   c - 234   c  of  FIG.  234   a    of a nasal cradle cushion of a patient interface in accordance with an example of the present technology. A patient&#39;s nose is shown in dashed lines. 
         FIG.  235   a    shows a top view of another nasal cradle cushion of a patient interface in accordance with another example of the present technology. 
         FIG.  235   b    shows a bottom cross-sectional view taken through line  235   c - 235   c  of  FIG.  235   a    of another nasal cradle cushion of a patient interface in accordance with another example of the present technology. 
         FIG.  235   c    shows a side cross-sectional view taken through line  235   c - 235   c  of  FIG.  235   a    of another nasal cradle cushion of a patient interface in accordance with an example of the present technology. A patient&#39;s nose is shown in dashed lines. 
         FIG.  236   a    shows a top view of another nasal cradle cushion of a patient interface in accordance with another example of the present technology. 
         FIG.  236   b    shows a bottom cross-sectional view taken through line  236   c - 236   c  of  FIG.  236   a    of another nasal cradle cushion of a patient interface in accordance with another example of the present technology. 
         FIG.  236   c    shows a side cross-sectional view taken through line  236   c - 236   c  of  FIG.  236   a    of another nasal cradle cushion of a patient interface in accordance with another example of the present technology. A patient&#39;s nose is shown in dashed lines. 
         FIG.  237   a    shows a top view of a nasal cradle cushion of a patient interface in accordance with an example of the present technology. 
         FIG.  237   b    shows a top view of a nasal cradle cushion of a patient interface in accordance with another example of the present technology. 
         FIG.  237   c    shows a top view of a nasal cradle cushion of a patient interface in accordance with another example of the present technology. 
         FIG.  237   d    shows a top view of a nasal cradle cushion of a patient interface in accordance with another example of the present technology. 
         FIG.  238   a    shows a cross-section of a nasal cushion taken through line  238   a - 238   a  of  FIG.  234   a    according to an example of the present technology. 
         FIG.  238   b    shows a cross-section of a nasal cushion taken through line  238   b ,  238   c - 238   b ,  238   c  of  FIG.  239    according to an example of the present technology. 
         FIG.  238   c    shows a cross-section of a nasal cushion taken through line  238   b ,  238   c - 238   b ,  238   c  of  FIG.  239    according to an example of the present technology. 
         FIG.  239    shows a top view of a nasal cradle cushion of a patient interface in accordance with an example of the present technology. 
         FIG.  240    shows a top view of a patient interface system according to an example of the present technology worn by a patient. 
         FIG.  241    shows a side view of a patient interface system according to an example of the present technology worn by a patient. 
         FIG.  242    shows an enlarged perspective view of a patient interface system according to an example of the present technology worn by a patient. 
         FIG.  243    shows an enlarged side view of a patient interface system according to an example of the present technology worn by a patient. 
         FIG.  244    shows an enlarged front view of a patient interface system according to an example of the present technology worn by a patient. 
         FIG.  245   a    shows a front perspective view of a seal-forming structure, plenum chamber, and retaining structure according to an example of the present technology. 
         FIG.  245   b    shows a top view of a seal-forming structure, plenum chamber, and retaining structure according to an example of the present technology. 
         FIG.  245   c    shows a bottom view of a seal-forming structure, plenum chamber, and retaining structure according to an example of the present technology. 
         FIG.  245   d    shows a side view of a seal-forming structure, plenum chamber, and retaining structure according to an example of the present technology. 
         FIG.  245   e    shows a rear view of a seal-forming structure, plenum chamber, and retaining structure according to an example of the present technology. 
         FIG.  245   f    shows a front view of a seal-forming structure, plenum chamber, and retaining structure according to an example of the present technology. 
         FIG.  245   g    shows a cross-sectional view of a seal-forming structure, plenum chamber, and retaining structure taken through line  245   g - 245   g  of  FIG.  245   f   , according to an example of the present technology. 
         FIG.  245   h    shows another front perspective view of a seal-forming structure, plenum chamber, and retaining structure according to an example of the present technology. 
         FIG.  245   i    shows a cross-sectional view of a seal-forming structure, plenum chamber, and retaining structure taken through line  245   i - 245   i  of  FIG.  245   b    according to an example of the present technology. 
         FIG.  245   j    shows a cross-sectional view of a seal-forming structure, plenum chamber, and retaining structure taken through line  245   j - 245   j  of  FIG.  245   f    according to an example of the present technology. 
         FIG.  245   k    shows a cross-sectional view of a seal-forming structure, plenum chamber, and retaining structure taken through line  245   k - 245   k  of  FIG.  245   c    according to an example of the present technology. 
         FIG.  246   a    shows a front perspective view of a patient interface system according to an example of the present technology. 
         FIG.  246   b    shows a view of a patient interface system from an inferior and posterior perspective according to an example of the present technology. 
         FIG.  246   c    shows a view of a patient interface system from a superior and anterior perspective according to an example of the present technology. 
         FIG.  246   d    shows a view of a patient interface system from an inferior and anterior perspective according to an example of the present technology. 
         FIG.  246   e    shows a side view of a patient interface system according to an example of the present technology. 
         FIG.  246   f    shows a bottom perspective view of a patient interface system according to an example of the present technology. 
         FIG.  246   g    shows another bottom perspective view of a patient interface system according to an example of the present technology. 
         FIG.  247   a    shows a top perspective view of a patient interface system according to an example of the present technology. 
         FIG.  247   b    shows a side view of a patient interface system according to an example of the present technology. 
         FIG.  247   c    shows a top perspective view of a patient interface system according to an example of the present technology. 
         FIG.  248 A  shows a perspective view of a frame for a patient interface and a detachable rigidiser arm according to an example of the present technology. 
         FIG.  248 B  shows a perspective view of a detachable rigidiser arm attached to a frame for a patient interface according to an example of the present technology. 
         FIG.  249 A  shows a perspective view of a frame for a patient interface and a detachable rigidiser arm according to an example of the present technology. 
         FIG.  249 B  shows a perspective view of a detachable rigidiser arm attached to a frame for a patient interface according to an example of the present technology. 
         FIG.  250 A  shows a perspective view of a frame for a patient interface and a detachable rigidiser arm according to an example of the present technology. 
         FIG.  250 B  shows a perspective view of a detachable rigidiser arm attached to a frame for a patient interface according to an example of the present technology. 
         FIG.  250 C  shows a rear perspective view of a frame for a patient interface and a detachable rigidiser arm according to an example of the present technology. 
         FIG.  251 A  shows a perspective view of a frame for a patient interface and a detachable rigidiser arm according to an example of the present technology. 
         FIG.  251 B  shows a perspective view of a detachable rigidiser arm attached to a frame for a patient interface according to an example of the present technology. 
         FIG.  252 A  shows a perspective view of a frame for a patient interface and a detachable rigidiser arm according to an example of the present technology. 
         FIG.  252 B  shows a perspective view of a detachable rigidiser arm attached to a frame for a patient interface according to an example of the present technology. 
         FIG.  252 C  shows a cross-sectional view of detachable rigidiser arm attached to a frame for a patient interface according to an example of the present technology taken through line  252 C- 252 C in  FIG.  252 B . 
         FIG.  253 A  shows a perspective view of a frame for a patient interface and a detachable rigidiser arm according to an example of the present technology. 
         FIG.  253 B  shows a perspective view of a detachable rigidiser arm attached to a frame for a patient interface according to an example of the present technology. 
         FIG.  253 C  shows a cross-sectional view of detachable rigidiser arm attached to a frame for a patient interface according to an example of the present technology taken through line  253 C- 253 C in  FIG.  253 B . 
         FIG.  254 A  shows a perspective view of a frame for a patient interface and a detachable rigidiser arm according to an example of the present technology. 
         FIG.  254 B  shows a perspective view of a detachable rigidiser arm attached to a frame for a patient interface according to an example of the present technology. 
         FIG.  255 A  shows a perspective view of a frame for a patient interface and a detachable rigidiser arm according to an example of the present technology. 
         FIG.  255 B  shows a perspective view of a detachable rigidiser arm attached to a frame for a patient interface according to an example of the present technology. 
         FIG.  256 A  shows a perspective view of a frame for a patient interface and a detachable rigidiser arm according to an example of the present technology. 
         FIG.  256 B  shows a perspective view of a detachable rigidiser arm attached to a frame for a patient interface according to an example of the present technology. 
         FIG.  256 C  shows a detailed top view of a detachable rigidiser arm attached to a frame for a patient interface according to an example of the present technology. 
         FIG.  257 A  shows a perspective view of a frame for a patient interface and a detachable rigidiser arm according to an example of the present technology. 
         FIG.  257 B  shows a perspective view of a detachable rigidiser arm attached to a frame for a patient interface according to an example of the present technology. 
         FIG.  258 A  shows a perspective view of a frame for a patient interface and a detachable rigidiser arm according to an example of the present technology. 
         FIG.  258 B  shows a perspective view of a detachable rigidiser arm attached to a frame for a patient interface according to an example of the present technology. 
         FIG.  259 A  shows a perspective view of a frame for a patient interface and a detachable rigidiser arm according to an example of the present technology. 
         FIG.  259 B  shows a perspective view of a detachable rigidiser arm attached to a frame for a patient interface according to an example of the present technology. 
         FIG.  259 C  shows a detailed rear perspective view of a frame for a patient interface and a detachable rigidiser arm according to an example of the present technology. 
         FIG.  260 A  shows a perspective view of a frame for a patient interface and a rigidiser arm according to an example of the present technology. 
         FIG.  260 B  shows a perspective view of a frame for a patient interface and a rigidiser arm according to an example of the present technology. 
         FIG.  261 A  shows a perspective view of a frame for a patient interface and a rigidiser arm according to an example of the present technology. 
         FIG.  261 B  shows a perspective view of a frame for a patient interface and a rigidiser arm according to an example of the present technology. 
         FIG.  262 A  shows a perspective view of a strap for a positioning and stabilising structure and a rigidiser arm for a patient interface system according to an example of the present technology. 
         FIG.  262 B  shows a perspective view of a strap for a positioning and stabilising structure attached to a rigidiser arm for a patient interface system according to an example of the present technology. 
         FIG.  263    shows a perspective view of a strap for a positioning and stabilising structure attached to a rigidiser arm for a patient interface system according to an example of the present technology. 
         FIG.  264 A  shows a perspective view of a rigidiser arm for a patient interface system according to an example of the present technology. 
         FIG.  264 B  shows a perspective view of a strap for a positioning and stabilising structure attached to a rigidiser arm for a patient interface system according to an example of the present technology. 
         FIG.  265    shows a perspective view of a strap for a positioning and stabilising structure attached to a rigidiser arm for a patient interface system according to an example of the present technology. 
         FIG.  266    shows a perspective view of a strap for a positioning and stabilising structure attached to a rigidiser arm for a patient interface system according to an example of the present technology. 
         FIG.  267    shows a perspective view of a strap for a positioning and stabilising structure attached to a rigidiser arm for a patient interface system according to an example of the present technology. 
         FIG.  268    shows a perspective view of a strap for a positioning and stabilising structure attached to a rigidiser arm for a patient interface system according to an example of the present technology. 
         FIG.  269    shows a perspective view of a strap for a positioning and stabilising structure attached to a rigidiser arm for a patient interface system according to an example of the present technology. 
         FIG.  270    shows a perspective view of a strap for a positioning and stabilising structure attached to a rigidiser arm for a patient interface system according to an example of the present technology. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLES OF THE TECHNOLOGY 
     Before the present technology is described in further detail, it is to be understood that the technology is not limited to the particular examples described herein, which may vary. It is also to be understood that the terminology used in this disclosure is for the purpose of describing only the particular examples discussed herein, and is not intended to be limiting. 
     Treatment Systems 
     In one form, the present technology comprises apparatus for treating a respiratory disorder. The apparatus may comprise a flow generator or blower for supplying pressurised respiratory gas, such as air, to the patient  1000  via an air circuit  4170  leading to a patient interface  3000 , as shown in  FIG.  1     a.    
     Therapy 
     In one form, the present technology comprises a method for treating a respiratory disorder comprising the step of applying positive pressure to the entrance of the airways of a patient  1000 . 
     Nasal CPAP for OSA 
     In one form, the present technology comprises a method of treating Obstructive Sleep Apnea in a patient by applying nasal continuous positive airway pressure to the patient. 
     Patient Interface  3000   
     Referring to  FIG.  166   , a non-invasive patient interface  3000  in accordance with one aspect of the present technology comprises the following functional aspects: a seal-forming structure  3100  (see, e.g.,  FIG.  4   ), a plenum chamber  3200 , a positioning and stabilising structure  3300  and a connection port  3600  for connection to a short tube  4180  of the air circuit  4170 . In some forms a functional aspect may be provided by one or more physical components. In some forms, one physical component may provide one or more functional aspects. In use the seal-forming structure  3100  is arranged to surround an entrance to the airways of the patient  1000  so as to facilitate the supply of air at positive pressure to the airways. 
     Seal-Forming Structure  3100   
     In one form of the present technology, the seal-forming structure  3100  provides a sealing-forming surface, and may additionally provide a cushioning function. 
     A seal-forming structure  3100  in accordance with the present technology may be constructed from a soft, flexible, resilient material such as silicone. The seal-forming structure  3100  may form part of a sealed path for air from a PAP device to be delivered to the nares of the patient. 
     Referring to  FIG.  9   , in one form of the present technology, the seal-forming structure  3100  may comprise a sealing flange  3110  and a support flange  3120 . The sealing flange  3110  may comprise a relatively thin member with a thickness of less than about 1 mm, for example about 0.25 mm to about 0.45 mm. The support flange  3120  may be relatively thicker than the sealing flange  3110 . The support flange  3120  is or includes a spring-like element and functions to support the sealing flange  3110  from buckling in use. In use the sealing flange  3110  can readily respond to system pressure in the plenum chamber  3200  acting on its underside to urge it into tight sealing engagement with the face, e.g., the patient&#39;s nares. The plenum chamber  3200  is made from a floppy material such as silicone. 
     Nasal Pillows 
     In one form of the present technology, the seal-forming structure  3100  of the non-invasive patient interface  3000  comprises a pair of nasal puffs, or a pair of nasal pillows  3130 , each nasal puff or nasal pillow being constructed and arranged to form a seal with a respective nares of the nose of a patient, e.g. by forming a seal against a peripheral region of the nares of the patient. 
     Nasal pillows  3130  ( FIG.  9   ) in accordance with an aspect of the present technology include: a frusto-cone  3140 , at least a portion of which forms a seal on an underside of the patient&#39;s nose e.g. a frusto-cone portion; a stalk  3150 , an upper flexible region  3142  on the underside of the frusto-cone  3140  and connecting the frusto-cone to the stalk  3150 . In addition, the structure to which the nasal pillow  3130  of the present technology is connected includes a lower flexible region  3152  adjacent the base of the stalk  3150 . Upper flexible region  3142  and lower flexible region  3152  can act in concert to facilitate a universal joint structure that is accommodating of relative movement—both displacement and angular—of the frusto-cone  3140  and the structure to which the nasal pillow  3130  is connected. In one example, the frusto-cone  3140  may be co-axial with stalk  3150  to which it is connected. In another example, the frusto-cone  3140  and the stalk  3150  may not be co-axial (e.g., offset). The nasal pillows  3130  may be dimensioned and/or shaped such that they extend out laterally beyond the walls of the plenum chamber  3200 , discussed below. 
     In one form of the present technology, each stalk  3150  may comprise a variable stiffness so as to prevent the nasal pillows  3130  from rocking forward during use due to compression and/or bending of the stalk  3150 . For example, the side of the stalk  3150  that is distal from the face of the patient in use may be stiffer than the region of the stalk  3150  proximal to the face of the patient. In other words, different material stiffness on opposing sides of the stalk  3150  presents more resistance if compression or bending of the stalk  3150  is not in a predetermined direction. This enables even compression of the pillows  3130  onto nares by preventing the pillows  3130  from rocking forward. Such an arrangement may be helpful in resisting buckling of the stalk  3150  that results in the nasal pillows  3130  rocking forward. The variable stiffness may also be used to provide a weak point about which rocking is facilitated such that the stalks  3150  buckle in a desired direction. In other words, even compression of the nasal pillows  3130  may be achieved. This arrangement may also allow the sealing force to be localized at the top of the nasal pillows  3130 . Additionally, this arrangement may also allow any deflection of the nasal pillows  3130  to be cantered thereon. The nasal pillows  3130  may also be formed to compress against the plenum chamber  3200  when urged against the face of the patient and because the nasal pillows  3130  may be laterally wider than the plenum chamber, no portion of the plenum chamber  3200  extends beyond the pillows  3130 . In another example, when compressed, the nasal pillows  3130  may be shaped and/or dimensioned so that their periphery is generally flush with the periphery of the plenum chamber  3200 . In a further example of the technology, the stalks  3150  may be thinnest at the base of the frusto-cone  3140 . 
     In an example, to engage the pillows  3130  with the entrance to the patient&#39;s airways, the pillows  3130  are placed at the entry to the nares. As the positioning and stabilising structure  3300  is adjusted, tension begins to pull the pillows  3130  into the nares. Continued insertion of the pillows  3130  into the nares causes the stalk  3150  to collapse via trampoline  3131  moving the base of pillows  3130  towards the upper surface of the plenum chamber  3200 . The stalks  3150  of the nasal pillows  3130  may be connected to the plenum chamber  3200  and comprise thinned or reduced thickness, portions. The thinned portions allow the pillows  3130  to easily spring, or trampoline, and therefore adjust to suit the alar angle of the patient  1000  more readily. The trampoline  3131  may be angled away from the bottom of the pillows  3130  or a septum and/or upper lip of the patient  1000 . This improves the comfort and stability of the patient interface device  3000 . 
     It is also envisioned that a variety of sizes of nasal pillows  3130  may be used with plenum chambers having a commonly sized connection region and plenum connection region. This has the advantage of allowing the patient to be fitted with a plenum chamber  3200  and pillows  3130  sized to best fit that patient&#39;s particular anatomy, e.g., size and orientation of the nares. 
     In one form of the present technology the seal-forming structure  3100  forms a seal at least in part on a columella region of a patient&#39;s nose. 
     Nasal Cradle 
     While a small portion of a nasal pillow  3130  may enter a patient&#39;s nares in use, an alternative form of seal-forming structure  3100  is substantially external of the nose in use. In one form of the present technology, shown in  FIG.  34   , the seal-forming structure  3100  of the patient interface  3000  is constructed and arranged to form a seal against the patient&#39;s airways that surrounds both nares without being entering the nares. The seal-forming structure  3100  may serve both nares with a single orifice, e.g. a nasal cradle. In  FIG.  34   , the seal-forming structure  3100  according to the depicted example includes a nasal flange  3101  disposed about its periphery. This view also indicates the attachment of the plenum chamber  3200  and seal-forming structure  3100  to the frame  3310 . 
     Nasal Cushion for Nasal Cradle 
       FIGS.  223  to  232    show several views of an exemplary patient interface system  3000  having a seal-forming structure  3100  in the form of a nasal cradle cushion.  FIGS.  233   a  to  233   h    show several views of an exemplary patient interface system  3000  having a seal-forming structure  3100  in the form of a nasal cradle cushion donned on a patient  1000 . The seal-forming structure  3100  may seal around the lower portion of the nose of the patient, particularly around the ala and tip of the nose. This seal-forming structure  3100  may define, at least in part, a gas chamber  3104 , which will be discussed in greater detail below. During therapy, breathable gas may be provided to the patient from the patient interface  3000  to the nose through the gas chamber  3104 . It should be understood that when the patient interface  3000  is donned on a patient, the seal-forming structure  3100  may, at least partially, along with the face of the patient, define the gas chamber  3104  through which breathable gas may be provided to the patient at positive pressure. For example, that the seal-forming structure  3100  in the form of a nasal cradle may seal below the nasal bridge (e.g., the transitional region between the bone and the cartilage of the nose), on or below the nose tip, the sides of the nose and/or the upper lip of the patient. According to another example of the present technology, the seal-forming structure  3100  in the form of a nasal cradle cushion may be structured to seal around an inferior periphery of the nose. In other words, seal may be formed with the lower surfaces of the patient&#39;s nose. It should also be understood that a nasal cradle cushion is different from nasal pillows because the nasal cradle cushion may serve both nares with a single orifice and may be structured so as not to enter the nostrils of the patient. The seal-forming structure  3100  may be a single wall cushion or the seal-forming structure  3100  may be dual wall cushion, e.g., the seal-forming structure may include an undercushion. Alternatively, the undercushion may be omitted and a rolled edge may be used around the opening of the seal-forming structure  3100  to form a secure pneumatic seal around the patient&#39;s nose. 
     A protruding end  3114  can be seen on either side of the seal-forming structure  3100 . When donned on the patient  1000  each protruding end  3114  may be shaped to extend from the patient interface  3000  so as to seal within the gap between the respective alae and nasolabial sulci of the patient.  FIG.  2   c   , which depicts superficial features of the face, indicates the location of the alae and the nasolabial sulci. The protruding ends  3144  may partially inflate and/or deform to seal in this area. A concave lower portion  3212  of the seal-forming structure  3100  inferior to the opening to the gas chamber  3104  may seal against the upper lip according to an example of the technology. The concave lower portion  3212  may be curved to substantially conform to a portion of the upper lip of the patient to form a seal in that region. The shape of the concave lower portion  3212  can be seen in  FIG.  245   c   , for example, where the seal-forming structure  3100  curves inwardly from the protruding ends  3114 . Since the upper lip of most patients is convex, the concave lower portion  3212  may easily conform to this region of the patient&#39;s face to form an effective seal. The posterior portion of the seal-forming structure  3100  inferior to the opening to the gas chamber  3104  that may seal against the upper lip of the patient may also be shaped and dimensioned not to cover the patient&#39;s nares when in use so as to ensure an uninterrupted pathway for the flow of pressurized gas into the patient&#39;s airways. According to another example of the present technology, the seal-forming structure  3100  may be softened, e.g., by reducing material thickness, at the posterior and inferior region of the seal-forming structure that seals against the patient&#39;s upper lip. 
       FIGS.  233   a  to  233   h    show how the exemplary patient interface  3000  may seal against a patient  1000 , particularly the nose. It should be understood that the seal-forming structure  3100  may be concave in shape to cradle the nose of the patient. A recessed portion  3116  may receive the tip of the patient&#39;s nose and the protruding end  3114  may seal in the region of the ala and nasolabial sulcus. The protruding ends  3114  may seal against the patient&#39;s face and nose at the region where the alae join to the face of the patient proximal to the nasolabial sulcus. (See  FIGS.  2   c ,  2   d , and  2   f   ) In most patients, this region is concave in shape and, thus, the protruding ends  3114  are intended to extend into and seal within this region. A protruding end support section  3208  may support the nasal cushion  3112  in the region of the protruding end  3114  to aid in maintaining the seal in this region, and may function like an undercushion. In an alternative example, the seal-forming structure  3100  may include rolled edge around the perimeter of the opening to the gas chamber  3104 , rather than including the protruding end support section  3208 . In a further alternative example, the seal-forming structure  3100  may not provided with a rolled edge or the protruding end support sections  3208 . 
       FIGS.  223  to  232    also show that the recessed portion  3116  may be included on the seal-forming structure  3100 . This recessed portion  3116  may comprise an inwardly shaped section that extends into the nasal gas chamber  3104  to receive the tip of the nose of the patient when donned by the patient. The recessed portion  3116  may provide enhanced sealing around and under the tip of the nose of the patient during therapy by allowing the shape of the seal-forming structure  3100  to better conform to the patient&#39;s nose. The seal-forming structure  3100  may also include an overhang near the recessed portion  3116  at the opening to the seal-forming structure that allows the seal-forming structure to better conform to and seal around the tip of the patient&#39;s nose. 
     The seal-forming structure  3100  may surround a portion of the nose, specifically the nose tip, of the patient  1000 . The gas chamber  3104  may be formed by the seal-forming structure  3100  and the face of the patient. 
     The patient interface  3000 , according to an example of the present technology, has a surface area footprint on the face which is less obtrusive than a conventional nasal face mask by a significant percentage. For some patients, it may also feel less claustrophobic. Also, the specific areas of reduced obstruction is important because these areas are found to have significant beneficial psychological impact on a bed partner when looking at the mask because it looks less medical and “opens up” the face. From the patient&#39;s perspective, the exemplary patient interface  3000  is not in or significantly reduced from their field of vision because the seal-forming structure  3100  seals below the bridge of the nose. This allows the patient to wear spectacles when reading a book or watching television after donning the patient interface  3000  before they fall asleep. By sealing below the nose bridge, irritation may be avoided in an area that has thin skin and pressure sensitive and high chance of skin breakdown due to blood flow constriction. Another advantage may be that anthropometric variations between patients above the nose bridge do not need to be considered and focus for the mask fit range can be directed towards anthropometric variations around the upper lip area. Also, unlike some other full face masks, the patient interface  3000  may not require a forehead support which may be required for providing pressure point relief. This may also avoid the problem of the forehead support being a source of pressure point and skin break down. This type of seal-forming structure  3100  may also be advantageous in that provides an alternative for respiratory therapy patients that do not find nasal pillows comfortable. 
     Anatomically,  FIGS.  2   h  and  2   i    may be referenced for an indication as to the location of the transitional region between the nasal bone and the cartilage that may be understood to define the bridge of the nose. Thus, the exemplary seal-forming structure  3100  may seal about the periphery of the nose of the patient in contact with the softer tissues of the nose, e.g., fatty tissue and cartilage. By forming a seal with the nose on these softer tissues it may be possible to avoid irritation of the skin of the patient that would otherwise occur were the seal to be formed around/over the harder nasal structures, i.e., bone. In other words, patient discomfort may be minimised by sealing below the bridge of the nose. Also, locating the seal of the seal-forming structure  3100  around this region of the nose may allow for an effective seal to be formed because the nasal tissues and the seal-forming structure  3100  may conform to one another to form the seal. The seal-forming structure  3100  may conform to the nose predominantly. 
     A sealing feature described above is the location of the protruding end  3114  against the face of the patient  1000 . Specifically, the protruding end  3114  may be an extended portion of the seal-forming structure  3100  that seals in the region between the nasolabial sulcus and ala. These anatomical features may be seen in  FIG.  2   c   . Depending on the individual facial structure of the patient, this region may represent a recessed portion such that an extension from the seal-forming structure  3100  may be necessary to form an adequate seal about the nose of the patient. The protruding ends  3114  may advantageously serve this function. 
     Another sealing feature of the exemplary patient interface  3000  is the recessed portion  3116  for the seal-forming structure  3100  to receive the tip of the nose of the patient  1000  when donned by the patient. Specifically, at the region where the recessed portion  3116  is located the tip of the nose of the patient  1000  can be seen in dashed lines, as shown in  FIGS.  233   a  to  233   h   . The seal-forming structure  3100  may be shaped to seal against the perimeter of the nose at its underside. In other words, the seal formed by the seal-forming structure  3100  against the nose may be characterized as against an inferior and peripheral portion of the nose. Thus, it may be understood that the sealing surface of the seal-forming structure  3100 , as a whole, may be concave or form a pocket to receive the nose and it may further include the recessed portion  3116  to receive the tip of the nose. 
     The seal-forming structure  3100  may seal against the nose of the patient  1000  at the tip. The gas chamber  3104  may be defined, at least in part, by the seal-forming structure  3100 , the plenum chamber  3200 , and the patient&#39;s nose to provide a sealed path for breathable gas to enter the patient&#39;s airways via the nares. 
     In an example, the seal-forming structure  3100  in accordance with the present technology is constructed from a soft, flexible, resilient material such as silicone. In another example of the present technology, the seal-forming structure  3100 , e.g., the seal-forming structure  3100  and its overhang  3206  may be formed from foam. The seal-forming structure  3100  may, according to further examples of the present technology, be formed from other materials including foam, gel, and/or low durometer silicone. 
       FIGS.  245   a ,  245   d , and  245   g - k   , show examples of the protruding end support sections  3208 . The protruding end support sections  3208  may be associated with respective protruding ends  3114  of the seal-forming structure  3100 . The protruding end support sections  3208  may also be understood to extend into the gas chamber  3104  defined, at least in part, by the seal-forming structure  3100  and the plenum chamber  3200 . Such a configuration may allow the protruding end support section  3208  to provide sufficient support for the protruding end  3114  to seal against the patient&#39;s face. 
     Protruding end support sections  3208  can be seen on either side of the seal-forming structure  3100 . The protruding end support section  3208  may be positioned under the protruding end  3114  of the seal-forming structure  3100 . The protruding end support section  3208  may be included to support the protruding end  3114  of the seal-forming structure  3100 . 
     The protruding ends  3114  may be included at each side of the seal-forming structure  3100 , as shown in  FIGS.  234   a    to  239 . The gas chamber  3104  and the opening thereto can also be seen. The opening to the nasal gas chamber  3104  may generally have a rectangular, lozenge or trapezoidal shape that may be curved at its respective minor sides  3104 . 2  and major sides  3104 . 1 ,  3104 . 3 , as shown in  FIGS.  237   a  to  237   d   . When placed against the nose of the patient the curved minor sides  3104 . 2  of the opening may be proximal to the respective alae of the nose. Also in this example, the distal major side  3104 . 1  of the opening, may be distal to the upper lip of the patient and near the tip of the nose, while the proximal major side  3104 . 3 , may be proximal to the upper lip of the patient. The recessed portion  3116 , shaped to receive the tip of the nose, is also shown. 
       FIGS.  234   a  to  234   c    show that the seal-forming structure  3100  may curve slightly upward as it approaches the distal major side  3104 . 1  of the opening to the gas chamber  3104  from the recessed portion  3116 . The front upper portion of the seal-forming structure  3100  that is near the recessed portion  3116  includes a slight dip or concave region at its center such that the seal-forming structure  3100  is higher at its sides than in the middle. This view also shows the outline of a nose in dashed lines to indicate how the nose of the patient may be located relative to the seal-forming structure  3100 . The peak  3118  in the seal-forming structure  3100  is tasked with sealing the front of the nares. The peak may sit further back, but may transition more gradually for creating the balloon effect to seal against the nares. The distal side  3104 . 1  may flick up from the seal-forming structure  3100  and may improve seal at the nose tip by making contact with the nose and may cause a compressive, pneumatic seal by cradling the nose. The recessed portion  3116  that is shaped to receive the tip of the nose is also shown. 
       FIGS.  235   a  to  235   c    also show the protruding ends  3114  at either side of the seal-forming structure  3100 . The profile of the seal-forming structure  3100  may slope downwardly as it approaches the distal side  3104 . 1  opening to the gas chamber  3104  from the recessed portion  3116 . This example of the seal-forming structure  3100  lacks the dip in the front region near the recessed portion. In other words, this example shows that the seal-forming structure  3100  may be more circular/rounder, relative to the example shown in  FIGS.  234   a  to  234   c    in the region from the recessed portion  3116  to the distal side  3104 . 1  of the opening to the gas chamber  3104 . 
       FIGS.  236   a  to  236   c    show that the shape of the opening to the gas chamber  3104  may be more balloon like and rounder than the examples shown in  FIGS.  234   a  to  234   c    and  FIGS.  235   a  to  235   c   . The seal-forming structure  3100  may have straight sidewalls, in contrast with sidewalls that curve smoothly from the upper surface of the seal-forming structure  3100 . The straight sidewalls may have a defined top edge and may increase stability and strength of the seal-forming structure  3100 . 
     In another example, the seal-forming structure  3100  may lack the dip in the front region near the recessed portion  3116 . The straight sidewalls of the exemplary nasal cushion  3112  may also be included. 
     Furthermore, it should also be understood that the exemplary seal-forming structures  3100  are shown in substantially undeformed states in  FIGS.  234   a - c ,  235   a - c , and  236   a - c   . Some drawings may indicate a small amount of deformation due to conformation with the shape of the nose shown in dashed lines. Thus, the seal-forming structures  3100  may have a concave shape as shown when not deformed. 
     It should also be understood that the seal-forming structure  3100  may have a cross-section of variable thickness, as shown in  FIGS.  238   a  to  238   c   . Thus, the region of the seal-forming structure  3100  proximate to the opening to the gas chamber  3104  may be thinner than the region where the seal-forming structure  3100  attaches to the plenum chamber  3200 . Advantageously, this may afford more comfort for the patient by providing a thinner and, thus, more compliant region of cushion material at the area where a large amount of contact is made with the patient&#39;s nose. 
     The region  3112 . 1  may be proximal to the opening to the gas chamber  3104  and the region  3112 . 3  may be proximal to the connection to the plenum chamber  3200 . The region  3112 . 2  may be the most elevated region around the upper periphery of the nasal cushion  3112 . 
     A smoothly variable thickness for the seal-forming structure  3100  from region  3112 . 1  to region  3112 . 3  is provided. Also, the thickness x may be less than the thickness z. The region  3112 . 2  may abruptly become thicker than the regions  3112 . 1  and  3112 . 3 . Also, the thickness x may be less than the thickness z and the thickness y may be greater than x and z. The region  3112 . 2  may abruptly become thicker than the regions  3112 . 1  and  3112 . 3 . Also, the thickness z may be less than the thickness x and the thickness y may be greater than x and z. 
       FIG.  239    shows another exemplary seal-forming structure  3100  according to the present technology, the opening to the gas chamber  3104  and the protruding end  3114  are indicated to allow for understanding of the orientation of the seal-forming structure  3100 . Regions of various thicknesses are hatched differently to better indicate where the thickness of the seal-forming structure  3100  may vary. Region  3113  may be the thinnest to allow for ready conformation to the tip of the nose. Region  3113 , according to an example of the present technology, may have a thickness of about 0.35 mm. Region  3115  may be thicker to provide more support for the seal-forming structure  3100 . Region  3115 , according to an example of the present technology, may have a thickness of about 0.5 mm. Region  3117  may be thicker than the other regions to provide maximum support, resistance to deformation, and ensure an effective seal at the ala of the patient. Region  3117 , according to an example of the present technology, may have a thickness of about 1 mm. 
     The bottom corners of the seal-forming structure  3100  may be stiffer relative to other areas of the seal-forming structure  3100  to prevent or minimise deformation at the bottom corners. Having a higher level of stiffness at the bottom corners of the seal-forming structure  3100  leads to a lower likelihood of seal disruption at these locations of the seal-forming structure  3100 , especially when tube torque is experienced. 
       FIGS.  245   a - k    depict further examples of the present technology. In these views the seal-forming structure  3100 , plenum chamber  3200 , and the retaining structure  3242  are shown disconnected from the frame  3310  (not shown in these views). These views show the protruding end support section  3208  that extends inward from the seal-forming structure  3100  and the plenum chamber  3200  to support the protruding ends  3114  when engaged with the nose of the patient. The protruding end support sections  3208  may be in the form of a hollow protrusion that extends into the interior of the patient interface  3000 . As can be seen in  FIG.  245   d   , the protruding end support section  3208  may be seen as a pocket formed in the side of the seal-forming structure  3100  and the plenum chamber  3200 . The protruding end support sections  3208  may be formed integrally with the seal-forming structure  3100  and the plenum chamber  3200 . In an alternative example, the protruding end support sections  3208  may not be hollow, but rather may be a solid extension formed integrally with the seal-forming structure  3100  and the plenum chamber  3200 . 
     It is also envisioned that the protruding end support sections  3208  may include additional supporting structures comprised of a material more rigid than the seal-forming structure  3100  and the plenum chamber  3200 . It should be understood that, according to one example of the present technology, that the sides of the protruding end support sections  3208  may spaced from the seal-forming structure  3100  and the plenum chamber  3200  when the patient interface  3000  is not sealingly engaged with the patient&#39;s nose. When the patient dons the patient interface  3000 , the seal-forming structure  3100  and the plenum chamber  3200  may be deformed and the protruding ends  3114  may be urged against the protruding end support sections, which in turn prevent the protruding ends from collapsing and support the protruding ends against the patient. For example, the protruding end support sections  3208  may support respective protruding ends  3114  as the protruding ends are deformed due to sealing engagement with the patient&#39;s face at the junction between the alae and the face. 
     Additionally, the protruding end support sections  3208  may have a profile such that the cross-sectional area of the protruding end support sections decreases as the protruding end support sections extend into the gas chamber  3104 . The end of the protruding end support section  3208  that extends into the gas chamber  3104  may also be flat as shown in  FIGS.  245   g  and  245   i - k    or, alternatively, the protruding end support section may come to a point. The walls that define the protruding end support sections  3208  may also increase or decrease in thickness toward the gas chamber  3204 . It is also envisioned that the protruding end support sections  3208  may have a profile that is curved. For example, the protruding end support sections  3208  may have a profile that is curved to substantially follow the profile of their respective protruding ends  3114 , while not directly contacting the protruding ends when the seal-forming structure  3100  is in a relaxed state. As can be seen in  FIGS.  245   g  and  245   i - k   , for example, the protruding end support sections  3208  may have a profile that is generally curved away from the respective protruding ends  3114  and toward the retaining structure  3242 . 
       FIGS.  245   f - h    show that the seal-forming structure  3100  may include thickened sections  3204 . These thickened sections  3204  may provide additional support for the seal-forming structure  3100  when it is in sealing engagement with the nose and the face of the patient. The thickened sections  3204  may be located on opposite sides of the seal-forming structure  3100  in a position such that they are proximal to the patient&#39;s nasolabial sulcus when the seal-forming structure engages the patient&#39;s face. The thickened sections  3204  may also help to seal around the alae of the patient&#39;s nose by preventing collapse of the seal-forming structure  3100  due to sealing forces. The thickened sections  3204  may be formed integrally with the seal-forming structure  3100 . Also, the thickened sections  3204  may be located on the seal-forming structure  3100  such that when the seal-forming structure engages the patient&#39;s nose and face the thickened sections  3204  may be, at least partially, urged against respective protruding end support sections  3208 . The thickened sections  3204  may have a constant thickness throughout that is greater than the thickness of the remainder of the seal-forming structure  3100 . Alternatively, the thickened sections  3204  may have a thickness that is variable across its area. 
       FIGS.  245   a ,  245   c - f ,  245   h ,  245   i , and  245   k    also show that the seal-forming structure  3100  may include an overhang  3206  to seal against the nose tip of the patient. The overhang  3206  may have a reduced thickness relative to the remainder of the seal-forming structure  3100  and the overhang may be positioned and structured to form a seal around the anterior portion of the patient&#39;s nose, e.g., the tip of the nose. The overhang  3206  may extend a substantial distance, for example, the overhang can be seen in the side view of  FIG.  245     d.    
       FIGS.  245   a ,  245   b ,  245   d - f ,  245   h ,  245   i , and  245   k    show examples of the seal-forming structure  3100  that may include a compliant region  3122 . The compliant region  3122  may be relatively soft, flexible, and/or compliant relative to other portions of the seal-forming structure  3100 . The compliant region&#39;s  3122  relative flexibility may be advantageous in that it may help to relieve discomfort to the patient in the regions of the tip of the nose and the septum. The compliant region  3122  may be relatively thin as compared to other portions of the seal-forming structure  3100  and, as such, may function like a mechanical spring to maintain an effective seal at the tip of the nose by wrapping against and/or contacting the tip of the nose. The compliant region  3122  may be located on the seal-forming structure  3100  at the upper apex where the seal-forming structure transitions to the plenum chamber  3200 , as can be seen in  FIG.  245   d    for example. The compliant region  3122  may be located on the seal-forming structure  3100  above the recessed portion. The compliant region  3122  may also blend into the recessed portion  3116 . The compliant region  3122  may also be located substantially centrally on the seal-forming structure in horizontal direction, as can be seen in  FIG.  245   e    for example. The seal-forming structure  3100  may have a thickness at the compliant region  3122  that is about 0.35 mm according to an example of the present technology and may be one of the thinnest regions of the seal-forming structure. 
     The views in  FIGS.  245   a - k    also show the retaining structure  3242  with notches  3295  and tongue portion  3211 . Additionally, these views show the sealing lip  3250 . 
     Also, the seal-forming structure  3100  may include visual indicators that are pad printed thereon to indicate to the patient the proper insertion depth of the nose. For example, the visual indicators may include an outline of a nose to show the patient where their nose should align relative to the seal-forming structure  3100 . Such visual indicators may indicate to the patient where to place the nose in the seal-forming structure  3100  so that they do not insert it too deep into the seal-forming structure, thereby resulting in a suboptimal seal. 
     Plenum Chamber  3200   
     Plenum chamber  3200  in accordance with an aspect of one form of the present technology functions to allow air flow between the two nares and the supply of air from PAP device  4000  via a short tube  4180 . The short tube  4180  is typically part of the air circuit  4170  that connects to the frame  3310  via a connection port  3600  and a longer tube (additional gas delivery tube)  4178  connected to the PAP device  4000 . In this way the plenum chamber  3200  may function alternatively as an inlet manifold during an inhalatory portion of a breathing cycle, and/or an exhaust manifold during an exhalatory portion of a breathing cycle. 
     Plenum chamber  3200  may be constructed from an elastomeric material. 
     Plenum chamber  3200 , in accordance with another aspect of one form of the present technology, provides a cushioning function between the seal-forming structure  3100  and the positioning and stabilising structure  3300 . 
     Whilst in one form of the plenum chamber  3200 , the inlet/outlet manifold and cushioning functions are performed by the same physical component, in an alternative form of the present technology, they are formed by two or more components. 
     The seal-forming structure  3100  and the plenum chamber  3200  may be formed, e.g. moulded, as a single and unitary component. 
     Plenum chamber  3200  comprises an anterior wall  3210  and a posterior wall  3220 . 
     Posterior wall  3220  comprises posterior surface  3222  (see  FIG.  8   ). In one form of the present technology, the seal-forming structure  3100  is constructed and arranged relative to the posterior wall  3220  so that in use, the posterior surface  3222  is spaced from a patient&#39;s septum and/or upper lip, as can be seen in  FIGS.  18  and  19   . In one form, e.g. when the seal-forming structure  3100  includes nasal pillows  3130 , this is achieved by arranging the posterior wall  3220  so that the posterior surface  3222  is anterior to a most posterior portion  3130 . 1  of the nasal pillow  3130 , as shown in  FIG.  8    by the posterior surface  3222 . This arrangement may also focus the sealing force on the nares of the patient  1000  because the septum and/or upper lip is relieved of contact with the patient interface  3000 . 
     The plenum chamber  3200  also comprises a flexing region  3230  ( FIG.  9   ), which forms a connection with seal-forming structure  3100 . The flexing region  3230  may be a distinct region from the anterior wall  3210  and/or the posterior wall  3220 . Alternatively some or all of the respective anterior wall  3210  and posterior wall  3220  may form part of flexing region  3230 . In one form of the present technology where the seal-forming structure  3100  comprises respective left and right nasal pillows  3130 , there is a corresponding respective left flexing region  3232  and right flexing region  3234  ( FIG.  4   ). Flexing regions  3230 ,  3232 , and  3234  are constructed and arranged to bend and/or flex in response to a force encountered in use of the patient interface  3000 , e.g., a tube drag force, or a movement of the patient&#39;s head, e.g., pushing the patient interface  3000  against a bed pillow. Flexing region  3230 , left flexing region  3232 , and/or right flexing region  3234  may be constructed from a silicone rubber, e.g., with a Type A indentation hardness in the range of about 35 to about 45. However, a wider range is possible if the thickness of the walls  3210 ,  3220  are adjusted accordingly to obtain a similar level of force. 
     Another aspect of the present technology that may be seen in  FIGS.  4 ,  7 ,  8 ,  10  and  11   , that the plenum chamber  3200  has a saddle or decoupling region  3236 . As can be seen in  FIG.  4   , the flexing region  3230  may comprise the decoupling region  3236 , which may be located between the left flexing region  3232  and the right flexing region  3234 . The decoupling region  3236  may be concave in shape and may span from the anterior wall  3210  to the posterior wall  3220 . By forming the plenum chamber  3200  with the decoupling region  3236  as described, it may be possible to decouple the left flexing region  3232  from the right flexing region  3234  such that movement in one of the flexing regions does not substantially affect the other flexing region. In other words, deformation and/or buckling of the left flexing region  3232  may not cause a disruption to the right flexing region  3234  and vice versa. Advantageously, this may allow the nasal pillow  3130  associated with the undisturbed flexing region to remain in position on the patient&#39;s corresponding naris in spite of a disruption to the other flexing region. The decoupling region  3236 , by being recessed between the stalks  3150 , may avoid contact with the septum. Also, the decoupling region  3236  may be the thinnest region of the plenum chamber  3200  to allow for the desired amount of flexibility in this region. Alternatively, the decoupling region  3236  may be the thickest region of the plenum chamber  3200 . By providing the saddle region  3236  with a deep curvature, septum and/or upper lip contact may be minimised or avoided to improve patient comfort. The saddle region  3236  may be U or V shaped and has a nasolabial angle at its peak of about 700 to about 120°. The saddle region  3236  may be about 0.5 mm to about 2.5 mm in depth for clearance around the patient&#39;s septum. 
     Posterior wall  3220  may be arranged, in use of patient interface  3000 , adjacent the superior or upper lip of the patient, as in  FIGS.  18  and  19   . 
     In one form, the plenum chamber  3200  may further comprise a sealing lip  3250  ( FIG.  6   ). Sealing lip  3250  may be constructed from a flexible resilient material, e.g. silicone rubber with a type A hardness in a range of about 30 to about 50, forming a relatively soft component. Sealing lip  3250  may be located on or formed as part of an interior surface or interior periphery of plenum chamber  3200 , or an entire interior peripheral region of plenum chamber  3200 , as shown in  FIGS.  5 ,  6  and  8   . However, it is also envisioned that the sealing lip  3250  may be disposed about an exterior surface or exterior periphery of the plenum chamber  3200 , or an entire exterior peripheral region of plenum chamber  3200 . Sealing lip  3250  may form a pneumatic seal between plenum chamber  3200  and frame  3310 , as will be described in greater detail below. Sealing lip  3250  and plenum chamber  3200  may also comprise one piece. Other patient interface devices form the pneumatic seal between the plenum chamber and frame using a compression seal to compress the plenum chamber made from a resiliently deformable material such as silicone to engage the plenum chamber to the frame and create the pneumatic seal at the same time. In contrast, one example of the present technology, forms a pneumatic seal when the plenum chamber  3200  is initially secured to the frame  3100  by interference from the sealing lip  3250  deflecting against the frame  3310 . When pressure within the plenum chamber  3200  is increased above atmospheric pressure for treating breathing disorders, the pneumatic seal is strengthened and increases the sealing force as the sealing lip  3250  is urged with greater force against the frame  3310 . The air pressure within the cushion/plenum chamber of these other patient interface devices does not influence the sealing force between the cushion and the frame. Also, these other patient interface devices have a cushion with side walls for engagement with the frame and sealing lips that are floppy because they readily conform to finger pressure, are not rigid, and are able to be stretched or bent elastically with little effort. In particular, due to the size and aspect ratio of a nasal cushion being relatively large, this contributes to the floppiness of the cushion. The side walls for frame engagement are so floppy that opposing sides of the cushion are able to be pinched together and brought into contact with each other with very little finger force. This ease of deformation of the side walls for frame engagement may be the primary source of difficulty for patients with arthritic hands to quickly connect the cushion to the frame in these other patient interfaces. It should also be understood that by forming the plenum chamber  3200  features discussed above with sufficient stiffness it may be possible to improve the stability of the seal made by the seal-forming structure. Furthermore, it may be possible to vary the thickness of the plenum chamber  3200  such that it becomes thinner from a plenum connection region  3240  to the seal-forming structure  3100 . In one example of the present technology, the plenum chamber  3200  may be about 2-3 mm thick near or at the plenum connection region  3240 , 1 mm thick at a point between the plenum connection region  3240  and the seal-forming structure  3100 , and 0.75 mm thick near or at the seal-forming structure  3100 . Forming the plenum chamber  3200  with these features may be accomplished by injection molding manufacturing. This gradual reduction in thickness of the plenum chamber  3200  enables greater deformability of silicone material closer to the stalks  3150  and patient&#39;s nose to enhance comfort and reduce the likelihood of seal disruption. 
     Some nasal pillow patient interfaces have an assembled order of (i), plenum chamber, (ii) headgear connection, and (iii) seal-forming structure. In contrast, one example of the patient interface  3000  of the present technology has an assembled order of (i) headgear connection, (ii) plenum chamber, and (iii) seal-forming structure. This difference in arrangement means that headgear tension does not cause deformation of the plenum chamber  3200  and the seal-forming structure  3100  which may lead to disruption of sealing forces. 
     Frame  3310   
     Frame  3310  functions as a central hub, as shown in  FIGS.  4 ,  10 ,  75 ,  76  and  166   , to which the short tube  4180 , plenum chamber  3200  and positioning and stabilising structure  3300  are connected, either in a removable fashion or a more permanent fashion. 
       FIGS.  31  to  33    also show various views of the frame  3310  connected to the positioning and stabilising structure  3300 , having straps  3301 , via a flexible joint  3305 . These views show the frame  3310  without the plenum chamber  3200  and the seal-forming structure  3100 . The connection port  3600  and the vent  3400 , both described in greater detail below, may be disposed on the frame  3310 . 
     In one example of the technology, the frame  3310  may be formed from polypropylene. 
     In another example of the technology, the frame  3310  may be made in one size but the plenum chamber  3200  and seal-forming structure  3100  may be made in multiple sizes that are attachable to the single frame by commonly sized connections features as described herein. 
     In an example of the technology the frame  3310  may be molded without any undercuts such that it may be molded and then removed from the mold tool without flexing. 
     Connection Between Plenum Chamber and Frame 
     In one form of the present technology, plenum chamber  3200  is removably attachable to frame  3310 , e.g., to facilitate cleaning, or to change for a differently sized seal-forming structure  3100 . This may permit the plenum chamber  3200  to be washed and cleaned more often than the frame  3310  and short tube  4180 . Also, it may permit the plenum chamber  3200  to be washed and cleaned separately from the strap  3301 . In an alternative form, plenum chamber  3200  is not readily removable from frame  3310 . 
     Plenum chamber  3200  may comprise the plenum connection region  3240  ( FIG.  6   ). A retaining structure  3242  of the plenum connection region  3240  has a shape and/or configuration that is complementary to a shape and/or configuration of a corresponding frame connection region  3312  ( FIG.  10   ). The retaining structure  3242  of the plenum chamber  3200  is more rigid than the other parts of the plenum chamber  3200 , and may be made from the same material as the frame  3310 , for example, polypropylene or polyamide such as Rilsan®. In other examples, the plenum connection region  3240  may be made from nylon, and the frame  3310  made from polypropylene. Nylon, polyamide and polypropylene are not floppy materials and do not readily conform to finger pressure. Therefore, when they are engaged to each other, there is an audible click and a hard to hard connection. The shape of the retaining structure  3242  is depicted in  FIGS.  20  to  24    in the form resembling a parabolic cylinder or hyperbolic cylinder. The retaining structure  3242  is not stretchable and inextensible in order to maintain its general shape as it engages and disengages from the frame  3310 . The shape of the retaining structure  3242  allows a slight degree of flexing but not to the extent that opposite sides of the retaining structure  3242  are able to touch each other if pinched together with finger pressure. In other words, the opposite sides of the retaining structure  3242  can only be brought into contact together with significant pinching force intended by the patient  1000  which would not occur under normal therapy circumstances. In the illustrated example, the top and bottom edges of the retaining structure  3242  are able to be pinched closer together/more easily together than the side edges of the retaining structure  3242  using the same amount of pinching force. As can be seen in  FIG.  18   , the curvature of the frame  3310  and retaining structure  3242  is intended to follow the natural curvature of patient&#39;s upper lip and may avoid concentration of contact pressure on any specific point of the patient&#39;s upper lip such that contact pressure from headgear tension is evenly spread over the patient&#39;s upper lip. This may minimise or eliminate skin breakdown caused by prolonged concentrated contact pressure. Another advantage for the curvature is that less material is required for the plenum chamber  3200  compared to a flat frame. A flat frame would result in more material for the plenum chamber  3200  at the side edges in order for the plenum chamber  3200  to conform to the patient&#39;s upper lip. Less material leads to an overall weight reduction for the patient interface  3000 . The curvature also minimises any protrusion of the patient interface  3000  in the anterior direction from the patient&#39;s face which improves the unobtrusiveness of the patient interface  3000 . Also, the retaining structure  3242  may be glued (e.g. using an adhesive) onto the plenum chamber  3200 , according to an example of the technology, after molding. In another example, an integral chemical bond (molecular adhesion) may be utilized between the retaining structure  3242  and the plenum chamber  3200 . 
     In an example of the technology, the retaining structure  3242  may be molded without any undercuts such that it may be molded and then removed from the mold tool without flexing. The retaining structure  3242  has a continuous peripheral edge on an anterior side that contacts the frame  3310 . This continuous peripheral edge is exposed so that it makes contact with the frame  3310  for engagement in a hard to hard manner. This is in contrast to a majority soft to hard connection where in some prior masks there is an anterior lip portion of the seal-forming structure that covers and overlaps the majority of a detachable rigid retaining structure. The anterior lip portion is made from LSR and wraps over the retaining structure to hold it together. However, in such prior masks, it is difficult and cumbersome to wrap the anterior lip portion over a detachable clip and possible for the clip to be misplaced which would then result in the inability of connecting the seal-forming structure to the frame. 
     One purpose of the retaining structure  3242  is to align the plenum chamber  3200  when engaging with the frame  3310  because the shape of the retaining structure  3242  of the plenum chamber  3200  is retained (possibly at varied depths) in a space defined between the frame connection region  3312  and interfering portion  3314  of the frame  3310  ( FIG.  29   ). 
     Another purpose of the retaining structure  3242  is to retain the plenum chamber  3200  to the frame  3310  by preventing relative lateral and vertical relative movement between these two parts. Plenum connection region  3240  may comprise at least one retention feature  3244 , and there may be at least one complementary frame connection region  3312 . Plenum connection region  3240  may comprise one or more retention features  3244  ( FIG.  10   ). In addition to preventing relative lateral and vertical movement between the plenum chamber  3200  and the frame  3310 , another purpose of the retention features  3244  is to prevent relative longitudinal movement between these two parts. The remaining portion of plenum chamber  3200  may comprise a more flexible material than the retaining structure  3242  and plenum connection region  3240 . 
     In one form, plenum connection region  3240  is constructed from a rigid or semi-rigid material, e.g. high durometer silicone or TPE, plastic, nylon, a temperature resistant material, polypropylene, and/or polycarbonate. Plenum connection region  3240  may be constructed from a different material to other portions of plenum chamber  3200 . For example plenum connection region  3240  may be a separate component that is permanently connected, integrally bonded or mechanically interlocked with connection portion  3202  ( FIG.  10   ) of the plenum chamber  3200 . Turning to  FIG.  6   , the connection portion  3202  of the plenum chamber  3200  may has substantially the same thickness as the retaining structure  3242  of the plenum connection region  3240 . Plenum connection region  3240  may include a tongue portion  3211  constructed and arranged to be matingly received by a channel portion  3211 . 1 , e.g., a channel portion of a frame  3310 . In this way, the channel portion  3211 . 1  may form a mating feature for the tongue portion  3211 , and vice versa. Also, the tongue portion  3211  and the channel portion  3211 . 1  may be dimensioned to maximize the sealing surface area in this region. 
     Attachment and removal of Plenum Chamber from Frame 
     The plenum chamber  3200  may be fixedly attached to the frame  3310 , but it also may be removably attached to the frame  3310 .  FIG.  12    shows the plenum chamber  3200  in a connected position relative to the frame  3310 . Plenum connection region  3240  includes in this example only two retention features  3244 , which are positioned on opposite sides of the connection region  3240 , e.g., on the posterior and anterior sides.  FIGS.  12  and  13    shows a cross-section that passes through both barbs  3246 , while  FIG.  17    shows another cross-section where the barbs  3246  are not present, forming e.g. a channel or groove  3211 . 1 . The resilient barbs  3246  are a type of snap-in compression-fit member to provide a high retention force (to prevent accidental disengagement) and also enable relatively easy intentional removal. In  FIG.  17   , the plenum connection region  3240  and the frame  3310  simply fit together in a tongue and groove like manner. The frame  3310  and retaining structure  3242  may be shaped so that the tongue portion  3211  and the channel portion  3211 . 1  engage before the retention features  3244  engage with the frame. This may help align the retention features  3244  for connection. 
     Each retention feature  3244  may take the form of a barb  3246  ( FIGS.  6  and  13   ) having a leading surface  3246 . 1  and a trailing surface  3246 . 2 . The leading surface  3246 . 1  is adapted to engage a lead-in surface  3312 . 1  of the frame connection region  3312  of the frame  3310 , as the plenum chamber  3200  and the frame  3310  are moved into engagement with one another. As the retention feature  3244  is pushed into position it deforms. Also, upper and lower regions of the frame connection region  3312  and interfering portion  3314  of the frame  3310  may also slightly deform. Also, the retaining structure  3242  may also slightly deform especially near the retention feature  3244  (for example, see broken line in  FIGS.  27  and  28   ). Turning to  FIGS.  195  to  198   , deformation of the frame connection region  3312  and interfering portion  3314  of the frame  3310  is controlled in terms of the amount of deformation permitted and also the areas of where deformation is to occur through the use of ribs  3294 . In one example of the present technology, there are six ribs  3294  spaced around and against the interfering portion  3314 . The spacing and position of the ribs  3294  limit the area of deformation of the interfering portion  3314  to only the area proximal to the retention features  3244 . The ribs  3294  may also abut and deform against the inner surface of the plenum connection region  3240  to provide a firmer engagement between the plenum connection region  3240  and the frame connection region  3312  at these contact points when the plenum chamber  3200  is engaged with the frame  3310 . Turning to  FIGS.  199  to  202   , the plenum connection region  3240  of the plenum chamber  3200  has notches  3295  to correspond with the ribs  3294 . The notches  3295  are chamfers to minimise the friction of the plenum connection region  3240  against the ribs  3294  during assembly of the plenum chamber  3200  with the frame  3310 . Once the barb  3246  is pushed in a sufficient amount, it snaps outwards in a radial sense such that the barb  3246  assumes a retained position shown in  FIG.  13   . The snapping action results in an audible sound to the user such as a re-assuring click sound, providing feedback to the user or patient that a proper connection has been established. In the retained position, the trailing surface  3246 . 2  of the barb  3246  engages with a retaining surface  3312 . 2  of the frame connection region  3312 , as shown in  FIG.  13   . This reassuring click sound may also be facilitated, in one example of the technology, by forming the plenum connection region  3240  of sufficient stiffness, that stiffness being greatest near the plenum connection region  3240 . This stiffness may be accomplished by overmolding manufacturing. 
     As can be seen in  FIG.  13   , the surfaces of the barb  3246  and the frame connection region  3312  are angled in certain manners to facilitate sliding connection between the plenum chamber  3200  and the frame  3310 . For example, as stated above, the leading surface  3246 . 1  and the lead-in surface  3312 . 1  may be formed with angles corresponding to one another such that these to surfaces may slidingly engage with one another with relative ease. Similarly, the trailing surface  3246 . 2  and the retaining surface  3312 . 2  may be angled relative to one another to help retain the frame  3310  and the plenum chamber  3200  once connected. The angles between the trailing surface  3246 . 2  and the retaining surface  3312 . 2  are selected such that a pulling force applied, e.g., generally along the axis of the nasal pillows  3130 , is sufficient to cause the barb  3246  to flex inwardly to thereby release the plenum chamber  3200  from the frame  3310 . This pulling force does not require the patient  1000  to first deflect the barbs  3246  radially inwards, e.g., by squeezing the plenum chamber  3200  in an anterior-posterior direction. Rather, due to the angles involved, the radial deflection of the barbs  3246  occurs solely as a result of the axial pulling force applied. In one example of the present technology, the plenum connection region  3240  is deflected and disassembly of the plenum chamber  3200  from the frame  3310  is performed by pinching the plenum chamber  3200  and pulling the plenum chamber  3200  away from the frame  3310 . 
     As can be seen in  FIG.  13   , the plenum chamber  3200  is attached to the frame  3310  via the plenum connection region  3240  and the retention feature  3244  is engaged with the frame connection region  3312  by the barb  3246 . Also shown in this view, the retaining surface  3312 . 2  of the frame connection region  3312  and the trailing surface  3246 . 2  of the barb  3246  are engaged and flush with one another. For the patient to detach the plenum chamber  3200  from the frame  3310  the patient must pull the plenum chamber  3200  with respect to the frame  3310  with sufficient force to overcome the resistance of the retaining surface  3312 . 2  against the trailing surface  3246 . 2 . In one example of the present technology, pinching the plenum chamber  3200  reduces the axial pulling force required to detach the plenum chamber  3200  from the frame  3310 . This resistance can be “tuned” or selectively adjusted to a desired level by varying the angle at which these surfaces  3312 . 2 ,  3246 . 2  engage with one another. The closer to perpendicular these surfaces  3312 . 2 ,  3246 . 2  are with respect to the direction of the force applied by the patient  1000  to detach the plenum chamber  3200  from the frame  3310 , the greater the force required to cause the detachment. This angle is shown as R in  FIG.  14   , where the trailing surface  3246 . 2  is angled with respect to a nominal vertical axis  3246 . 4  (corresponding to axial pull direction of plenum chamber  3200  to the frame  3310 ). As R is increased, the force required to detach the plenum chamber  3200  from the frame  3310  rises. Furthermore, as R increases the detachment will feel more abrupt to the patient  1000 . In one example, an angle R of approximately 75 degrees has been found to generate a comfortable feel of detachment for the patient. In further examples, R may vary from 30 to 110 degrees or from 40 to 90 degrees or from 65 to 85 degrees to generate an ideal level of resistance to detachment. This has been selected to minimise the likelihood of accidental detachment, and to only permit intentional detachment by the patient  1000 . 
     Angle α, the angle between the nominal vertical axis  3246 . 4  and the leading surface  3246 . 1 , can likewise be “tuned” or selectively adjusted to require a specific level of force when the patient  1000  attaches the plenum chamber  3200  to the frame  3310 . As angle α is increased, the force required to engage the retention feature  3244  with the frame connection region  3312  increases and the feeling of attachment for the patient engaging these components  3244 ,  3312  becomes more abrupt. In other words, as the leading surface  3246 . 1  of the retention feature  3244  slides along the lead-in surface  3312 . 1  of the frame connection region  3312  the user may experience a smoother feel of engagement as angle α decreases. In one example, an angle α of approximately 30 degrees has been found to generate a comfortable feel of attachment for the patient  1000 . In further examples, angle α may vary from 50 to 70 degrees or from 15 to 60 degrees to generate an ideal level of resistance to attachment. 
     Furthermore, since the feel and force of engagement and disengagement of the plenum chamber  3200  and frame connection region  3312  can be tuned or selectively adjusted independently of one another, angles α and β may be chosen to cause the patient to feel a level of resistance to attachment that is different from the level of resistance of detachment. In one example of the technology, angles α and β may be chosen such that angle β is greater than angle α, such that the patient feels less resistance to attachment of the plenum chamber  3200  and frame  3310  than resistance to detachment. In other words, it may feel harder for the patient to disconnect the plenum chamber  3200  from the frame  3310  than to connect them. 
     As can be seen in  FIG.  4   , one example of the technology includes a pair of retention features  3244 ,  3245 . Also shown in this view, the exemplary retention features  3244 ,  3245  are differently sized. Particularly, this view shows that the retention feature  3245  disposed on an anterior portion of the plenum connection region  3240  is narrower than the retention feature  3244  disposed on the posterior portion of the plenum connection region  3240 . By sizing the retention features  3244  differently, the patient  1000  is only able to attach the plenum chamber  3240  to the frame  3310  in one orientation. Such an arrangement is shown in  FIG.  10   . This avoids patient frustration during attachment, minimises damage to the patient interface  3000  that may arise from incorrect attachment, ensures the seal-forming structure  3100  is in the correct orientation to provide a proper seal against the patient&#39;s airways and provide comfort by reducing or avoiding contact with a septum and/or an upper lip of the patient  1000 . 
     In  FIG.  10    two frame connection regions  3312 ,  3313  are shown in engagement with corresponding retention features  3244 ,  3245 . The example depicted here shows that the narrower anterior retention feature  3245  is sized to correspond to the narrower anterior frame connection region  3313 . Also, the wider posterior retention feature  3312  is engaged with the correspondingly sized posterior frame connection region  3244 . An arrangement such as this, where one retention feature is uniquely dimensioned to engage with a corresponding uniquely dimensioned frame connection region, has the advantage that the patient will only be able to attach the plenum chamber  3240  to the frame  3310  in one orientation. By limiting the orientations of attachment, the patient  1000  is prevented from assembling the patient interface  3000  improperly and receiving suboptimal therapy due to an improperly assembled patient interface  3000 . The arrangement described with respect to this particular example of the technology is advantageous to the patient  1000  that may have difficulty seeing how to correctly engage the components due to vision problems or the patient  1000  who may be assembling the patient interface  3000  in a dark room, e.g., the bedroom before sleep, because the patient  1000  will only be able to completely assemble the patient interface  3000  if the components are properly aligned. 
     As described above, the angles of the leading surface  3246 . 1  and the trailing surface  3246 . 2  on the barb  3246  are important to providing an optimum amount of resistance to assembly and disassembly of the patient interface  3000 . Also described above is the benefit of sizing respective retention features  3244 ,  3245  and frame connection regions  3312 ,  3313  correspondingly such that a proper orientation of the components is ensured upon assembly Properly dimensioning the retention features  3244 ,  3245  and the frame connection regions  3312 ,  3313  may help to guide the plenum chamber  3200  onto the frame  3310 . In other words, the frame connection regions  3312 ,  3313  and the retention features  3244 ,  3245  may be dimensioned in close conformity to one another such that the perimeter of the frame connection regions and the perimeter of the retention features  3244  to aid in directing and aligning the retention feature  3244  into the frame connection region  3312 . This may be beneficial to a patient with limited dexterity due to a disease (e.g., arthritis) or a patient assembling the patient interface  3000  where visibility is diminished whether in a dark bedroom prior to sleep or due to limited vision. Also, by dimensioning the retention features  3244 ,  3245  and the frame connection regions  3312 ,  3313  in close conformity to one another this serve to ensure that the seal between the plenum chamber  3200  and the frame  3310  is maintained by facilitating a secure connection between these two components. Additionally, close conformity between the retention features  3244 ,  3245  and the frame connection regions  3312 ,  3313  may serve to facilitate equal alignment of the plenum chamber  3200  on the frame  3310 . In one example of the present technology a difference of 0.3 mm to 2 mm may be incorporated between the retention features  3244 ,  3245  and the frame connection regions  3312 ,  3313 . 
     It should also be understood that connection between the frame  3310  and the plenum chamber  3200  described above and below may be used with other types of masks. Such features may be applicable to nasal or full-face masks as well. Masks that seal under the bridge of the nose, such as compact nasal masks or compact full-face masks, may also incorporate the connection features described herein. Furthermore, masks that lack a forehead support may also include these connection features. It is also envisioned that examples of the present technology that include masks that seal below the tip of the nose, such as those with nasal pillows  3130  or a nasal cradle/nasal flange  3101 , may also use these connection features. 
     Plenum Chamber and Frame Attachment and Removal Sequence 
       FIGS.  25  to  29    show a sequence of cross-sectional views of the connection portion  3202  of the plenum chamber  3200  and the frame connection region  3312  of the frame  3310 . These sequential views show the process of attachment of the plenum chamber  3200  to the frame  3310 . While these views show only the attachment of one retention feature  3244  to one frame connection region  3312 , it should be understood that there may be more than one retention feature  3244  and more than one frame connection region  3312 , as can be seen in  FIG.  10    and discussed above. Therefore, during the attachment sequence of the plenum chamber  3200  and the frame  3310  there may be more than one instance of the depicted attachment sequence taking place to accomplish complete attachment of the plenum chamber  3200  and the frame  3312 . 
       FIG.  25    shows a cross-sectional view of the connection portion  3202  of the plenum chamber  3200  and the frame connection region  3312  of the frame  3310  where the connection portion  3202  and the frame connection region  3312  are near one another but not in contact. The arrow indicates that the connection portion  3202  and the frame connection region  3312  are being brought together. It should be understood that for these views additional portions of the plenum chamber  3200  and the frame  3310  have not been included in the interest of simplicity. Thus, it should also be understood that frame connection region  3312  and interfering portion  3314  of the frame connection region  3312  are both part of the frame  3310  as can be seen, for example, in  FIG.  13   . Moreover, it should be understood then that the frame connection portion  3312  and the interfering portion  3314  of the frame connection portion  3312  will move relative to one another through the attachment sequence. Returning to  FIG.  25   , this view shows that the sealing lip  3250  is not deformed and the retention feature  3244  is not deformed as neither of these components  3250 ,  3244  are in contact with the frame  3310 . 
       FIG.  26    shows the barb  3246  of the retention feature  3244  beginning to make contact with the frame connection region  3312  of the frame  3310 . Specifically, this view shows the leading surface  3246 . 1  of the barb  3246  in contact with the lead-in surface  3312 . 1  of the frame connection region  3312 . In this view, the retention feature  3244  and the frame connection region  3312  are only just coming into contact with one another such that the retention feature  3244  is not deflected. Also, the sealing lip  3250  has not been deflected because it is not yet in contact with the interfering portion  3314  of the frame connection region  3312 . As described above, the angle α of the leading surface  3246 . 1  will begin to affect the resistance the user will feel to engagement of the plenum chamber  3200  and the frame connection region  3312  because the leading surface  3246 . 1  will begin to engage in frictional contact with the lead-in surface  3312 . 1 . 
       FIG.  27    shows the plenum chamber  3200  and the frame  3310  further along in the attachment sequence such that the retention feature  3244  is deflected by contact with the frame connection region  3312 . As can be seen in this view, the frame connection region  3312  and the interfering portion  3314  of the frame connection region  3312  are nearer to the connection portion  3202 . Also shown in this view, the leading surface  3246 . 1  of the barb  3246  is in contact with a portion of the lead-in surface  3312 . 1  that is closer to the retaining surface  3312 . 2 . In other words, the barb  3246  can be seen having moved closer to attachment with the frame connection region  3312  and having moved relative to the position shown in  FIG.  26   . As described earlier, the connection portion  3202  and the plenum connection region  3240  of the plenum chamber  3200  may also be deflected from a pinching force generated by the patient  1000 .  FIG.  27    also indicates that the retention feature  3244  has been deflected by contact with the frame connection region  3312  and the dashed lines show the outline of the retention feature  3244  in an undeformed state.  FIG.  27    also shows that the sealing lip  3250  is not yet in contact with the interfering portion  3314  of the frame connection region  3312 , and, therefore, the sealing lip  3250  is not deformed. Although, not shown in this view it should also be understood that the frame connection region  3312  may deflect away from the retention feature  3244  due to the force of these parts  3312 ,  3244  being forced together. 
     In  FIG.  28    the plenum chamber  3200  and the frame  3310  are nearly attached and the retention feature  3244  is nearly completely engaged with the frame connection region  3312 . In this view the retention feature  3244  is still deformed but the barb  3246  is in contact with a different portion of the frame connection region  3312 . Specifically, the trailing surface  3246 . 2  of the barb  3246  is now in contact with the retaining surface  3312 . 2  of the frame connection region  3312 . Also, due to the fact that the angle at which the trailing surface  3246 . 2  and the retaining surface  3312 . 2  contact one another, the retention feature  3244  and the frame connection region  3312  may be urged into engagement by the inherent tendency of the deflected retention feature  3244  to return to its undeformed state, in effect drawing these parts together after a certain insertion distance is reached.  FIG.  28    also shows the outline of the retention feature  3244  in an undeformed state with dashed lines. Also in this view it can be seen that the sealing lip  3250  is in contact with the interfering portion  3314  of the frame connection region  3312 . At this point in the attachment sequence a seal may begin to be formed by the contact of the sealing lip  3250  and the interfering portion  3314  of the frame connection region  3312 . The sealing lip  3250  may also be slightly deflected by contact against the interfering portion  3314  of the frame connection region  3312 . 
       FIG.  29    shows the plenum chamber  3200  and the frame  3310  fully attached by engagement of the barb  3246  of the retention feature  3244  with the frame connection region  3312 . In this view the retaining surface  3312 . 2  may be relatively flush against the trailing surface  3246 . 2 . The retention feature  3244  may also no longer be deflected by contact with the frame connection region  3312 . The retention feature&#39;s  3244  return to an undeformed state from its deflected or deformed state, as shown in  FIG.  28   , may generate an audible click as the barb  3246  and the retention feature  3244  move to the position shown in  FIG.  29    from the position shown in  FIG.  28   . This re-assuring audible click may be advantageous in that it provides the patient  1000  with feedback that the plenum chamber  3200  and the frame  3310  are fully engaged. By providing the patient  1000  with this feedback upon completion of engagement the patient  1000  may be able to use the patient interface  3000  with confidence that the plenum chamber  3200  and the frame  3310  are securely attached and will not separate while the patient  1000  is asleep and receiving therapy. 
     Furthermore, a desired level of sealing contact may be achieved when the plenum chamber  3200  and the frame  3310  are attached as shown in  FIG.  29   . The sealing lip  3250  can be seen deflected against the interfering portion  3314  of the frame connection region  3312 . By being deflected as shown, the sealing lip  3250  may be urging itself against the interfering portion  3314  of the frame connection region  3312  with sufficient force due to the tendency of the sealing lip  3250  to return to its undeformed state such that a desired seal is generated between these components. Furthermore, as air pressure within the plenum chamber  3200  increases when therapy is applied, the sealing lip  3250  is forced to deflect towards the portion  3314  of the frame connection region  3312  thereby increasing the sealing force in this area. Even though a compression seal is formed between the retaining structure  3242  and frame connection region  3312  when the plenum chamber  3200  is engaged with the frame  3310 , a pressure-activated seal also is formed between sealing lip  3250  and the portion  3314  of the frame connection region  3312  on engagement which strengthens as air pressure within increases. It may be possible in certain examples that the compression seal is not air tight resulting in undesired leakage. 
     Also, if a very large amount of compression of components is required to form the compression seal, this may hinder easy attachment and detachment of the plenum chamber  3200  to the frame  3310  possibly requiring more than a single hand to perform the operation or a significant amount of effort. Therefore, in one example of the present technology, the compression seal functions predominantly for the purpose of retention rather than of seal, and the pressure-activated seal functions predominantly for the purpose of creating and maintaining an air tight seal. It should be understood that such a sealing effect may be occurring about the periphery of the junction between the plenum chamber  3200  and the frame  3310 . For example,  FIG.  17    shows the sealing lip  3250  in a similarly deflected state against the frame connection region  3312  at a region separate from the retention features  3244 . Moreover, it can be seen in  FIG.  5   , for example, that the sealing lip  3250  extends around the perimeter of the plenum chamber  3200 . By extending the sealing lip  3250  inwardly around the perimeter of the junction between the plenum chamber  3200  and the frame  3310  the desired level of sealing can be achieved throughout this region, thereby preventing undesired leakage of pressurized gas. 
     Additionally, it should be understood that the sealing lip  3250  may be pressing against the interfering portion  3314  of the frame connection  3312  with a force that is urging these parts to separate. However, the friction force due to structural engagement of the trailing surface  3246 . 2  of the barb  3246  with the retaining surface  3312 . 2  of the frame connection region  3312  should be sufficient to resist the force of the sealing lip&#39;s  3250  tendency to return to an undeformed state and separate the plenum chamber  3200  from the frame  3310 . 
     As for removal of the plenum chamber  3200  and the frame  3310 , it should be understood that this process is substantially the reverse order of the process described above. In other words, the user may separate the plenum chamber  3200  from the frame  3310  by pulling these components in opposite directions and the view of  FIG.  29    may be the beginning of the separation process and  FIG.  25    may represent the view wherein the plenum chamber  3200  and the frame  3310  are fully separated. Pinching of the plenum chamber  3200  proximal to the plenum connection region  3240  or pinching the plenum connection region  3240  and pulling away from the frame  3310  may assist in removal of the plenum chamber  3200  from the frame  3310 . It is also envisaged that the patient  1000  may pinch the plenum chamber  3200  for the purpose of gripping it, at any location, for example, the nasal pillows  3130  or stalks  3150  and simply pull it away from the frame  3310 . A twisting motion while pulling may also assist in disengaging the plenum chamber  3200  from the frame  3310 . 
     Hard-to-Hard Connection 
     The plenum connection region  3240  and the frame  3310  may be assembled and attached as shown in  FIGS.  25  to  29   . As stated above, the plenum connection region  3240  and/or retaining structure  3242  may be comprised of a semi-rigid material, e.g., high durometer silicone (a higher durometer than plenum chamber  3200 )/TPE, plastic, nylon, polypropylene, polyamide and/or polycarbonate. The plenum connection region  3240  can be constructed in the form of a continuous ring or oval, two C-shaped clips, one C-shaped clip, or a single continuous piece but only surrounding a part of the plenum chamber  3200 . The clip may function as a spring clip and be in the form of a C-section or double C-section. The spring force of the spring clip may be provided by resiliency of the plenum connection region  3240  being stretched against the frame connection regions  3312 ,  3313  or interfering portion  3314  of the frame  3310 . In another example, a clip form may be not be necessary and only the retention features  3242 ,  3244  are permanently and directly connected to the plenum chamber  3200  without a plenum connection region  3240  and/or retaining structure  3242  for engagement with the connection regions  3312 ,  3313 . It is also envisioned that one example of the present technology may also include the frame  3310  being comprised of the same or a similar semi-rigid material as the plenum connection region  3240 . By manufacturing the frame  3310  and the plenum connection region  3240  of semi-rigid material, a “hard-to-hard” connection or bonding interface may be created. This “hard-to-hard” connection, in conjunction with the structural features of the plenum connection region  3240  and the frame connection region  3312 , may provide the patient  1000  with a confident feeling (e.g., by providing an audible snap fit or re-assuring click sound) of the connection between the plenum chamber  3200  and the frame  3310  when assembling the patient interface  3000 . Since a secure fit between the plenum chamber  3200  and the frame  3310  is helpful to ensure that the patient  1000  receives optimal therapy through the patient interface  3000 , a design that provides the patient  1000  with confidence that a secure fit has been achieved is beneficial. A hard-to-hard connection as described herein may also be beneficial in that it may add stability to the seal made by the seal-forming structure  3100 . This is contrast to a hard-to-soft or a soft-to-soft connection where either or both the plenum chamber and frame are made of a floppy material which makes it difficult for arthritic hands to properly engage the plenum chamber and frame easily, especially in darkened room. 
     Although the retention features  3242 ,  3244  are described as provided on the plenum chamber  3200  and the connection regions  3312 ,  3313  are provided on the frame  3310 , it may be possible to switch the location to the retention features on the frame and the connection regions on the plenum chamber. Also, there may be a combination of a retention feature and a connection region on one part that corresponds with a connection region and a retention feature on the other part. 
     Method of Making the Plenum Chamber 
     A process to manufacture plenum chamber  3200  may comprise the step of moulding plenum connection region  3240  in a first tool, removing moulded plenum connection region  3240  from the first tool, inserting the plenum connection region  3240  into a second tool, and moulding a portion of plenum chamber  3200  comprising connection portion  3202  in the second tool. Plenum connection region  3240  may be chemically bonded and/or mechanically interlocked to connection portion  3202 . 
     In one form, the sealing lip  3250  is constructed and arranged to interfere with the interfering portion  3314  ( FIG.  13   ) of frame connection region  3312  when plenum chamber  3200  and frame  3310  are assembled together. In use, sealing lip  3250  is caused to resiliently flex away from a resting position ( FIG.  6   ) when assembled with the interfering portion  3314  of frame connection region  3213 , and at least in part as a result of being a resilient material, pushes against the interfering portion  3314  ( FIG.  12   ) to resist or prevent leakage of air between sealing lip  3250  and the interfering portion  3314 . Although the sealing lip  3250  has been described as provided with the plenum chamber  3200 , the sealing lip may be provided on the frame  3310 . Although one sealing lip has been described, it is possible two or more sealing lips may be provided, with at least one with the plenum chamber  3200  and at least one with the frame  3310 . 
     Positioning and Stabilising Structure  3300   
     Note that in one form of the present technology, a number of structural features form part of a positioning and stabilising structure  3300 , e.g., a headgear assembly (which may be referred to simply as headgear). In an alternative form of the present technology, one or more of those features are located on the frame  3310 . For example, a flexing joint  3305  may be wholly or partly located on the headgear, or on the frame  3310 . Also, the extension  3350  may perform the same function as the flexing joint  3305  except that it is integrally formed with the rigidiser arm  3302 . 
     The seal-forming structure  3100  of the patient interface  3000  of the present technology may be held in sealing position in use by the positioning and stabilising structure  3300  ( FIGS.  75 ,  76  and  166   ). In one form, the positioning and stabilising structure  3300  comprises headgear. It should be appreciated that the positioning and stabilising structure  3300  may, in one form of the technology, be referred to as headgear. 
     Headgear may be removably connectable to a portion of the patient interface such as the positioning and stabilising structure  3300  via a headgear connector. 
     Straps 
     The positioning and stabilising structure  3300  may comprise at least one strap  3301  (see, e.g.,  FIG.  65   ) and at least one rigidiser arm  3302  (see, e.g.,  FIG.  67   ). The strap  3301  may be made of an elastic material and may have elastic properties. In other words, the strap  3301  may be elastically stretched, e.g., by a stretching force applied by the patient and, upon release of the stretching force, returns or contracts to its original length in a neutral state. The strap  3301  may be made of or comprise any elastomeric material such as elastane, TPE, silicone etc. The material of the strap  3301  may also represent a combination of any of the above materials with other materials. The strap  3301  may be a single layer or multilayer strap. The strap  3301 , particularly the side strap portions  3315 ,  3316  in contact with the patient  1000  during use, may be woven, knitted, braided, molded, extruded or otherwise formed. The strap  3301  may comprise or may be made of a textile material such as a woven material. Such material may comprise artificial or natural fibers for, on the one hand, providing desired and beneficial surface properties such as tactile properties and skin comfort. On the other hand, the material of the strap  3301  may include elastomeric material for providing the desired elastomeric properties. The entire strap  3301 , including the side strap portions  3315 ,  3316  and back strap portion  3317 , may all be stretchable. This enables the entire length of the strap  3301  to be stretched which leads to a comfortable force displacement profile. In order for the strap  3301  to be stretched in use, the length of the strap  3301  may be less than the average small head circumference of patients. For example, the length of the strap  3301  may be less than 590 mm in one example and less than 500 mm in another example. However, straps  3301  of different lengths may be provided to patients depending on their head circumference which may be gender specific. For example, a small sized strap may be 490 mm in length and a large sized strap may be 540 mm. In some circumstances this means that the length of the strap  3301  need not be stretched by a large distance (i.e. small sized strap for a large head circumference) which would have unnecessarily high headgear tension for such patients and also a less smooth force displacement profile as the small sized strap  3301  is being stretched to longer lengths. 
     According to alternative examples of the present technology, the strap  3301  may be inelastic or may not be able to stretch substantially. The rigidiser arms  3302  may or may not be included. According to these alternative examples, the length of the strap  3301  of the positioning and stabilising structure  3300  may be adjustable with ladder lock clips, buckles or a hook and loop materials. The strap  3301  may be formed from a substantially inelastic material such as a plastic or a textile. The use of an inelastic strap  3301  may be beneficial in that seal stability may be more easily maintained when the seal-forming structure  3100  is a nasal cradle cushion and tube torque is experienced by the patient interface  3000 . 
     The strap  3301  is rigidised at a certain sections, for example, from the frame  3301  up to a position proximal to the patient&#39;s cheekbone by the inserted rigidiser arms  3302 . The strap  3301  may take the form of a hollow ribbon. The strap  3301  may be considered to be threaded over the rigidiser arm  3302  when it is slipped onto the rigidiser arm  3302  and secured at one end of the rigidiser arm  3302  proximal to the frame  3301 . 
     In one example, the strap  3301  including the side strap portions  3315 ,  3316  and back strap portion  3317  are made by warp knitting a textile material. The strap  3301  is a 3D knitted fabric that is knit by computer control as a single unitary piece. Variation in the thread and stitching may occur at various positions along the strap  3301  to adjust the elasticity and strength and durability of the strap  3301  at certain locations. For example, at the locations of the openings, insertion points or button-holes  3303 ,  3304  and the bifurcation point  3324  for the back strap portions  3317   a ,  3317   b , an additional thread may be knitted to provide reinforcement of the strap  3301  to prevent failure/breakage of the strap  3301  at these locations that subject to high stress when the strap  3301  is stretched during repeated and prolonged use. Both the knitting method (i.e. warp knitting) and the elastic textile material (e.g. elastane) of the strap  3301  contribute to the elastic recovery of the strap  3301  after washing the strap  3301  in water and dried. In other words, the elasticity of the strap  3301  can be maintained after prolonged use by periodically washing the strap  3301  and therefore its operational life is extended. 
     In  FIGS.  65  to  73   , the strap  3301  is shown as being a single continuous strap with two pocketed ends  3311 ,  3313  for being attached, directly or via a flexible joint  3305 , to a frame  3310 . However, it may be appreciated that the strap  3301  may comprise multiple individual straps which are or may be directly connected to one another, for example, stitching or ultrasonic welding. In  FIG.  65   , the strap  3301  and positioning and stabilising structure  3300  is shown without any adjustment or variation means. Such adjustment may be provided, however, by varying where the strap  3301  is secured to a patient interface  3000  or other connection elements more rigid than the strap  3301  such as a flexible joint  3305 . Turning to  FIG.  72   , in addition or alternatively, adjustment could be allowed by adding a mechanism, such as slide over ladder lock clips  3305 . 1  on the back  3317  or side strap portions  3315 ,  3316  (as shown, e.g., in  FIGS.  71  to  73   ) or by otherwise adjusting the elastic length of the strap  3301  and positioning and stabilising structure  3300 , respectively. In the example shown in  FIG.  65   , the strap  3301  has a tube-like configuration as can be taken from the respective schematic views in  FIGS.  68  to  70    indicating an oval or circular shape or respective marks  3321   a - d ,  3323   a - e  of circular or oval shape indicating the (visible) outer surface facing towards the viewer as solid and the (invisible) inner wall facing away from the viewer in dashed lines, as well as by the cross-sectional view according to  FIG.  66   . However, it will be appreciated that the positioning and stabilising structure  3300  may take any other shape such as flat or sheet-like shape, single, multi-layer or laminate construction. The strap  3301  may have a longitudinal axis which may be understood to be the axis substantially parallel to the paper plane, along which the strap  3301  extends (see, e.g., dashed line in  FIG.  65   ). 
     The strap  3301  have may reinforced stitching to improve durability and minimise or prevent failure points. For example, the areas of the strap  3301  at the button-holes  3303 ,  3304  and also at the location where it bifurcates into two back strap portions  3317   a ,  3317   b , at bifurcation points  3324 , are subject to high stress when stretched. The tendency of the material is to split away from each other at a split region  3326  and therefore reinforced stitching at these areas is one way to address this concern. In an example, a central seam runs along the centre longitudinal axis of the strap  3301  and functions as reinforced stitching. Also, the distal edges of the strap  3301  and the opening at the button-holes  3303 ,  3304  may be ultrasonically welded to fuse any stray fibers and strengthen the strap  3301  in these regions. Advantageously, this also prevents fraying of the fibers of the strap  3301  after extended use and repeated washing. Other techniques are envisaged for reinforcing and strengthening the pocketed end  3311 , distal edges and button-hole  3303 , which may include additional material such as tape. The tape may include branding and logo information also. 
       FIGS.  123  to  125    show increasingly detailed views of the split region  3326  between the upper back strap portion  3317   a  and the lower back strap portion  3317   b . The edges of the upper back strap portion  3317   a  and the lower back strap portion  3317   b  should be understood to not be perfectly smooth as a result of the knitting process and it should be further understood that these views show the edges with a great deal of magnification such that imperfections are visible. With the naked eye the undulations on the edges of the upper back strap portion  3317   a  and the lower back strap portion  3317   b  would not be so easily visible and are not generally discernible by the patient  1000  by touch. Additionally, stippling is used in these views to show the texture of the back strap portions  3317   a ,  3317   b  while the split region  3326  is shown blank because the split region  3326  is an absence of material. 
       FIGS.  126  to  131    show various detailed views of the bifurcation point  3324  that exists where the upper back strap portion  3317   a  and the lower back strap portion  3317   b  split off from a side strap portion  3315 ,  3316 . Also visible in these views is a reinforced portion  3325  that may include additional stitching or welding at or proximal to the bifurcation point  3324 . The reinforced portion  3325  may aid in preventing the side strap portions  3315 ,  3316  from splitting and/or tearing due to stress from the repeated separation of the upper back strap portion  3317   a  and the lower back strap portion  3317   b . In other words, the reinforced portion  3325  may provide additional strength at a location of stress concentration near the bifurcation point  3324 . Also shown in these views are the upper back strap portion  3317   a  and the lower back strap portion  3317   b  at various angles of separation θ. These views may be understood to show that the reinforced portion  3325  provides additional strength at the bifurcation point  3324  when the upper back strap portion  3317   a  and the lower back strap portion  3317   b  are spread from one another at large angles θ. 
     Referring to  FIGS.  176  to  181   , in one example of the present technology, the ends of the strap  3301  have a reinforcement portion  3327  with a material folded over the end of the strap  3301 . This provides further reinforcement in this area in addition to the welded ends  3311 . 1 ,  3313 . 3  (see  FIG.  81   ). The material of the reinforcement portion  3327  may be a different material to the strap  3301 . The reinforcement portion  3327  may avoid or mitigate the likelihood of a patient  1000  tearing or ripping the strap  3301  along its longitudinal axis beginning from this area. The reinforcement portion  3327  helps provide a visual and tactile indication to the patient  1000  on how to slip on or remove the strap  3301  from the rigidiser arm  3302  because it may assist in identifying the location of the button-hole  3303 ,  3304 . The corners  3328  of the reinforcement portion  3327  have been cut and are rounded so that the corners  3328  approximately match the rounded corners of the rigidiser arm  3302  at its distal free ends  3302 . 1  (see  FIGS.  50 ,  52 ,  55 ,  57 ,  58 ,  60   ). This provides a snug fit with the rigidiser arm  3302  which is more aesthetically pleasing. The rounded corners  3328  provide a soft edge to avoid facial scratching that could occur if they were sharp corners instead. 
     Rigidiser Arms 
       FIG.  67    shows an example of a rigidiser arm  3302 . As shown, the rigidiser arm  3302  may take a crescent or semi-circular shape. The rigidiser arm  3302  may have a generally elongate and flat configuration. In other words, the rigidiser arm  3302  is far longer and wider (direction from top to bottom in the paper plane) than thick (direction into the paper plane). The rigidiser arm  3302  has a three-dimensional shape which has curvature in all three axes (X, Y and Z). Although the thickness of the rigidiser arm  3302  may be substantially uniform, its height varies throughout its length. The purpose of the shape and dimension of the rigidiser arm  3302  is to conform closely to the cheeks of the patient in order to remain unobtrusive and frame the patient&#39;s face and cheeks. The ends  3319   a ,  3319   b  of rigidiser arm  3302  may be rounded and/or slightly angled relative to the remainder of the rigidiser arm  3302 . While the rigidiser arm  3302  may be flat, as indicated by the paper plane in  FIG.  67   , it will be appreciated, that the rigidiser arm  3302  may have a desired spatial configuration also in the direction into the paper plane in  FIG.  67   , particularly in order to allow improved alignment with the shape of a patient&#39;s face, such as the shape of a patient&#39;s cheek or head side region (see, e.g.,  FIGS.  71  and  72   ). The rigidiser arm  3302  may have a longitudinal axis which may be understood to be the axis substantially parallel to the paper plane, along which the rigidiser arm  3302  extends (see dashed line in  FIG.  67   ). 
     The rigidiser arm  3302  is more rigid than the strap  3301  and less rigid than the mask frame  3310 . In particular, the rigidiser arm  3302  and/or the strap  3301  are such that in combination the rigidiser arm  3302  imparts a shape, and an increased degree of rigidity in at least one direction or in or around at least one axis, to the strap  3301 . Also, the rigidiser arm  3302  guides or defines the direction or path of stretch for the strap  3301 . In other words, the patient stretches the strap  3301  in a direction substantially parallel to the longitudinal axis of the rigidiser arm  3302 . Stretching of the strap  3301  in other directions leads to rotation of the rigidiser arm  3302  relative to the mask frame  3310  which is undesirable. The rigidity of the rigidiser arm  3302  biases the rigidiser arm  3302  towards its natural, unrotated, untwisted and undeformed state. To some degree, this enables the positioning and stabilising structure  3300  to be self-adjusting headgear. The self-adjusting function avoids manually shortening or lengthening the material length of headgear straps and then remembering the adjusted length. This has typically been a cumbersome process because headgear straps on both sides of the face have to be shortened or lengthened one at a time. It may remove the ability for patients to over tighten the headgear when such high levels of headgear tension is not required to maintain a good sealing force. In the shown example, strap  3301  has a tube- or sleeve-like configuration. In other words, the strap  3301  is hollow in order to receive the insertion of the rigidiser arm  3302  which is slid into the strap  3301  via the button-hole  3303 . In another example, the rigidiser arm  3302  may be permanently connected to the strap  3301  at least in one location, for example, at the anchor point it is overmolded or glued to form an integral chemical bond (molecular adhesion) between the rigidiser arm  3302  and the strap  3301 . 
     Strap  3301  comprises side strap portions  3315 ,  3316  and a back strap portion  3317  located between the side strap portions  3315 ,  3316 . Side strap portions  3315 ,  3316  are adapted to extend along the sides of a patient&#39;s head when being worn while back strap portion  3317  is adapted to extend along the back of a patient&#39;s head, as shown in  FIGS.  4  to  8  and  166   . Back strap portion  3317  may be comprised of two, three or more straps arranged in parallel, particularly for providing stability. Although the smaller back strap portions  3317   a ,  3317   b  have been illustrated as equal in length, it is envisaged that one back strap portion is longer than the other back strap portion. The greater the number of smaller back strap portions  3317   a ,  3317   b  for the back strap portion  3317 , the greater the spring effect provided. In other words, as the number of same sized smaller back strap portions  3317   a ,  3317   b  increases when the strap  3301  is manufactured, the more tension is exerted on the side strap portions  3315 ,  3316  to be pulled closer to each other by the back strap portions  3317   a ,  3317   b . In the shown example, side strap portions  3315 ,  3316  of strap  3301  bifurcate into two back strap portions  3317   a ,  3317   b . In one example, each back strap portion  3317   a ,  3317   b  has half the amount of elastane material compared to each side strap portion  3315 ,  3316  of the strap  3301 . In one example, the positioning and stabilising structure  3300  is connected to the mask frame  3310  by a removable connection between strap  3301  and the rigidiser arm  3302  via a button-hole  3303 ,  3304  and the rigidiser arm  3302  being permanently connected to the mask frame  3310  via mechanical interlock. In another example, a flexible joint  3305  made from TPE may permanently connect to the rigidiser arm  3302  and the mask frame  3310 . The flexible joint  3305  is overmolded with the mask frame  3310  for permanent connection and the flexible joint  3305  is permanently connected to the rigidiser arm  3302  via mechanical interlock. In another example, the flexible joint  3305  may be made from the same material as the rigidiser arm  3302 , for example, Hytrel®, and is integral with the rigidiser arm  3302  and the flexible joint  3305  is permanently connected to the mask frame  3310  via mechanical interlock. The strap  3301  is removably connected with the rigidiser arm  3302  via a button-hole  3303 ,  3304 . 
     The engagement of the strap  3301  to the rigidiser arm  3302  may occur in one location proximal to the mask frame  3310 . This type of engagement allows for a maximum range of motion i.e. stretching of the strap  3301 . This engagement is removable to enable the strap  3301  to be fully detachable from the rigidiser arm  3302  and in turn, the mask frame  3310  to facilitate washing of the strap  3301 . The engagement functions as an anchor point for the strap  3301  such that when the strap  3301  is stretched, the stretching force is directed outwardly away from the anchor point. Turning to  FIGS.  48  to  60   , the end of the strap  3301  at the anchor point is retained by at least the distal edge of the rigidiser arm  3302  and/or a protruding end  3306  extending from the rigidiser arm  3302 . 
     It will be appreciated by the skilled person that the rigidiser arm  3302  as referred to herein may be more rigid than the strap  3301  and allows the rigidiser arm to impart a shape to the strap  3301 . The rigidiser arm  3302  may be more rigid in or around at least one axis and is inextensible in contrast to the strap  3301  which can be stretched along at least one axis. In another example, the rigidiser arm  3302  is extensible/stretchable in a direction substantially parallel to its longitudinal axis. Although elastomers typically can stretch, some thermoplastic polyester elastomers do not stretch but are flexible, for example, Hytrel® 5556 manufactured by DuPont®. For example, the rigidiser arm  3302  may have a scissor linkage structure or telescopic structure which enables the rigidiser arm  3302  to move between a compressed position to a fully elongated position. An extensible rigidiser arm  3302  may allow a better fit for patients  1000  who have longer faces so that the length of the rigidiser arm  3302  can be adjusted appropriately. Alternatively, the rigidiser arm  3302  may be referred to as a yoke and/or a stiffener. A yoke may be understood to be a rigid element adapted to support the straps  3301  of the positioning and stabilising structure  3300 . A rigidiser arm  3302  may be understood to be a rigid element shaping the straps  3302  of the positioning and stabilising structure  3300  when worn on the face. 
     Alternative Rigidiser Arms 
       FIGS.  223  to  232    show an exemplary patient interface system  3000  discussed above.  FIGS.  233   a  to  233   h    show such an exemplary patient interface system  3000  donned on a patient.  FIGS.  240 - 244    show further views of an exemplary patient interface system without the straps  3301  to show features of the rigidiser arms  3302  included therewith. The patient interface system  3000  shown in these views may include rigidiser arms  3302  to ensure an effective seal by the seal-forming structure  3100  against the nose of the patient. It should be understood that the seal-forming structure  3100  described above in relation to  FIGS.  223  to  239    may be included in the exemplary patient interface  3000  with the rigidiser arms  3302  shown in these drawings. 
     The rigidiser arms  3302  may be designed to minimize twisting and it may be stiffer than the rigidiser arms  3302  described elsewhere herein. The stiffer rigidiser arms  3302  may be advantageous to include with the seal-forming structure  3100  in the form of a nasal cradle cushion because the stiffer rigidiser arms may ensure an effective seal with this type of seal-forming structure. In the examples having nasal pillows as the seal-forming structure  3100 , the nasal pillows may help to locate and retain themselves against the nares by extending into the nares. In the examples where the seal-forming structure  3100  is a nasal cradle cushion such a retention function may not as easily achieved. Thus, the rigidiser arms  3302  may be provided with the patient interface system  3000  having a nasal cradle cushion as a seal-forming structure  3100  to ensure that the seal-forming structure can maintain an effective seal against the patient&#39;s nose. According to an example of the present technology, the extensions  3370 ,  3371  may be configured to prevent movement of the rigidiser arms  3302  in a plane parallel to the patient&#39;s sagittal plane (see  FIG.  2   f   ) and/or the extensions may be configured to allow the rigidiser arms to flex in a plane parallel to the patient&#39;s Frankfort horizontal (see  FIG.  2   e   ). In other words, the rigidiser arms  3302  may flex outwardly and inwardly relative to the patient&#39;s face more easily to accommodate various face widths, compared to vertical movement relative to the mask frame  3310 . In one example, the rigidiser arms  3302  may only be permitted to flex outwardly and inwardly relative to the patient&#39;s face and unable to or highly resistive to movement in any other direction in order to increase the stability of the patient interface  3000  especially when tube torque is experienced in the sagittal plane. 
     According to examples shown in  FIGS.  240 - 244   , the exemplary rigidiser arms  3302  may be connected to the mask frame  3310  by a mechanical interlock facilitated by overmolding the frame  3310  over a portion of extensions  3370 ,  3371 . The rigidiser arms  3302  may also include a joint  3374  to connect the rigidiser arms  3302  with the extensions  3370 ,  3371 . The rigidiser arms  3302  may be formed in one piece and of one material with the joints  3374  and the extensions  3370 ,  3371 . The material selected for the rigidiser arms of these examples may be like the material used for rigidiser arms of other examples discussed elsewhere herein. Likewise, the frame  3301  may be formed of the same material used with other examples disclosed herein. Thus, the overmolded connection may be necessary to join the extensions  3370 ,  3371  to the frame  3310  because the respective materials may not be able to be bonded together. The respective materials of the rigidiser arms  3302  and the frame, as well as the overmolded connection, are described in greater detail below. 
     The extensions  3370 ,  3371  may, in the example using a nasal cradle cushion as the seal-forming structure  3100 , be made wider in a vertical direction than the extensions  3350  used in examples having nasal pillows. The additional bulk of the larger extensions  3370 ,  3371  may provide the resistance to twisting, discussed above, that may be beneficial with the use of a nasal cradle cushion. This may be the case because in either example, the same material is used for the rigidiser arms  3302 , however, more material is necessary in the nasal cradle cushion example to provide the desired increase in stiffness. According to an example of the present technology, the extensions  3370 ,  3371  may have a width substantially equal to a width of a main body  3333  of the rigidiser arms  3302  at the widest portion of the main body in a vertical direction to achieve the desired stiffness and resistance to twisting. According to another example of the present technology, the extensions  3370 ,  3371  may be wider than the main body  3333  of the rigidiser arms  3302  in a vertical direction to achieve the desired stiffness and resistance to twisting. Alternatively, the extensions  3370 ,  3371  may be formed with reinforcing ribs, the extensions may be formed with a geometric shape more resistant to twisting, and/or the rigidiser arms  3302  may be formed from stiffer material(s). 
     It should also be understood that the rigidiser arms  3302  of the examples using a nasal cradle cushion for the seal-forming structure  3100  may also be fitted with the straps  3315 ,  3316  in similar fashion to the examples using nasal pillows, as shown in  FIGS.  223  to  233     h . This arrangement is described in greater detail elsewhere herein. 
     The right-side extension  3370  shown in these drawings also includes indicia  3372  that may be raised from the extension to provide the patient with a visual and tactile reference for properly orienting the patient interface  3000  when donning the patient interface for therapy. 
       FIGS.  246   a - g    show several views of an exemplary patient interface  3000 . These views show the patient interface  3000  without the straps  3301  of the positioning and stabilising structure  3300  and without the short tube  4180 . 
       FIGS.  246   e - g    show views of the patient interface  3000  in which the protruding end support section  3208  is visible. 
     The rigidiser arms  3302  may also be used as a visual indicator for the patient as to the proper insertion depth of the nose into the seal-forming structure  3100 . For example, length of the rigidiser arms  3302  could be an indication of the proper position of the patient interface  3000  relative to the ears such that the seal-forming structure is optimally located against the nose, thereby forming an effective seal. 
     Attachment of Straps and Rigidiser Arms 
     The side strap portions  3315 ,  3316  of strap  3301  shown in  FIG.  65    each include two button-holes  3303 ,  3304 . The button-holes  3303 ,  3304  may be located at the outer surface of strap  3301 , i.e., the surface facing away from the patient  1000  when being worn, and are adapted to receive rigidiser arm  3302  in order to insert the rigidiser arm  3302  into the interior of the tube- or sleeve-like strap  3301  or to remove it therefrom. Alternatively, the button-holes  3303 ,  3304  may be located at the inner surface of the strap  3301 . The button-holes  3303 ,  3304  may be oriented and/or shaped such that the rigidiser arm  3302  may be inserted and/or removed through such button-hole  3303  in order to assemble the positioning and stabilising structure  3300  while still preventing accidental removal or separation of the rigidiser arm  3302  from the strap  3301  during use. As shown in  FIG.  65   , this may be achieved by providing button-holes  3303  having a slit-like configuration, e.g., similar to button-holes, which may be oriented alongside or transversely to the strap  3301 . Alternatively, the button-holes  3303  may be oriented across the strap  3301  if required. In other words, the elongate extension of the button-hole  3303 ,  3304  may extend substantially coaxial to the longitudinal axis of both strap  3301  and rigidiser arm  3302 . This allows, particularly due to the elasticity of strap  3301 , an easy insertion of the rigidiser arm  3302  into the tube- or sleeve-like strap or part of strap  3301  while, at the same time, preventing its accidental removal. An end portion of the strap  3301  between the distal tip of the strap  3301  and the button-hole  3303  wraps over the edge of the rigidiser arm  3302  and functions an anchor point. This edge of the rigidiser arm  3302  or anchor point may be a catching member. This end portion of the strap  3301  may also be referred to as the pocketed end  3311 . This prevents the strap  3301  from slipping off the inserted rigidiser arm  3302  when the strap  3301  is stretched and adjusted while donning or doffing the patient interface  3000 . 
     Referring to  FIGS.  185  and  186   , the rigidiser arm  3302  may be inserted into the first button-hole  3303  of the strap  3301 . Said another way, the strap  3301  may be slipped over the rigidiser arm  3302  via the button-hole  3303 . The distal free end  3302 . 1  of the rigidiser arm  3302  is first inserted into the strap  3301  via the button-hole  3303 . The rigidiser arm  3302  is pushed further inside the strap  3301  until most or substantially the entire rigidiser arm  3302  is inserted into the strap  3301  such that the end portion of the strap  3301  can securely anchor to the edge of the rigidiser arm  3302 . Some material of the strap  3301  near the button-hole  3303  is adjusted to sit beneath the outer side  3319  of the protrusion  3309  (see  FIG.  38   ). Once inserted in the strap  3301 , the rigidiser arm  3302  may be left floating generally unrestricted inside the strap  3301 , as can be seen in  FIGS.  6  to  8   . Most importantly, the button-hole  3303  should be above the attachment point because the end portion of the strap  3301  is caught against the protruding end  3306  of the rigidiser arm  3302  to secure the strap  3301  to the rigidiser arm  3302  and also pulls against the protruding end  3306  when the strap  3301  is stretched. Typically, the position of the attachment point between the rigidiser arm  3302  and strap  3301  is more important than the type of attachment, for example, using a button-hole  3303 ,  3304  in the strap  3301 . Referring to  FIGS.  182  to  184   , the type of attachment between the rigidiser arm  3302  and strap  3301  may facilitate easy removal of the strap  3301  from the rigidiser arm  3302  to enable separate washing of the strap  3301 . In other words, the washing and cleaning regime for the strap  3301  may be at different times from the mask frame  3310 . The patient  1000  slightly stretches the strap  3301  around the button-hole  3303  to unfasten the strap  3301  from the rigidiser arm  3302 . After the distal end of the strap  3301  is unfastened, the strap  3301  may be pulled off completely from the rigidiser arm  3302  via the button-hole  3303 . 
     In addition or alternatively, the rigidiser arm  3302  is affixed to the strap  3301 . The affixing may be effected by attaching or affixing the second end of the rigidiser arm  3302 , which after the insertion is near the button-hole  3303 , to the strap  3301  of the positioning and stabilising structure  3300 . The fixation may be localized, as discussed in the introductory portion of the description. Here, the connection between the rigidiser arm  3302  and the strap  3301  is not distributed along the length of the strap  3301 , but is localized in the area adjacent to the button-hole  3303 . Alternatively, such connection may be established in the area adjacent to the button-hole  3304 . The affixing may be performed by way of sewing, welding, gluing, heat staking, clamping, buttoning, snapping a cover over the end or snapping on an external part by pushing the rigidiser arm  3302  inside the strap  3301  and fixing both the strap and the rigidiser arm  3302  to an external component, such as an external clip that holds both the strap and the respective end of the rigidiser arm  3302 . The strap  3301  may alternatively be chemically bonded to the rigidiser arms  3302 . The clip may also be used to attach the end of the strap  3301  to a respective end of a mask frame  3310 . As such, the clip may be a part of the mask frame  3310  itself. 
     With the present technology, while the strap  3301  is arranged to take the shape of the rigidiser arm  3302 , it is still able to stretch substantially along its entire length. Thus, the rigidiser arm  3302  imparts the required shape which directs the pressure of the positioning and stabilising structure  3300  to the required portions of the face, while the elastic positioning and stabilising structure  3300  maintains its entire operational length and is able to freely stretch over the rigidiser arm  3302 . Additionally, the rigidiser arms  3302  may decouple tube torque in the coronal plane. Also, in particular, the sharp bend  3307  of the rigidiser arms  3302  may serve to handle and decouple any tube torque in the sagittal plane. At the same time, the strap  3301  of the positioning and stabilising structure  3300  may cover the rigidiser arm  3302  and provides a soft feel and enhanced comfort. 
     The sharp bend  3307  provides stability for the patient interface  3000 . If the patient  1000  is sleeping on their side, the rigidiser arm  3302  against the side of the face on the bedding is pushed inwardly. The sharp bend  3307  decouples this movement in the coronal plane to prevent disruption of the seal force. The sharp bend  3307  has a tighter turn on its upper surface (facing away from the patient&#39;s face) compared to its lower surface (facing the patient&#39;s face). The lower surface of the sharp bend  3307  has a larger radius (washed out) than the upper surface of the sharp bend  3307  which smooths it out and avoids or minimises facial marking on the patient  1000  since the contact pressure is less concentrated if there is any contact on the patient&#39;s septum and/or upper lip (from nose droop caused by tube weight or tube torque). The distance between the two sharp bends  3307  is about 50 mm 
     Although being shown and discussed with regard to the specific examples shown in  FIGS.  65  to  70   , it will be appreciated that strap  3301 , or each of the strap side strap portions  3315 ,  3316  may be provided with one button-hole  3303 ,  3304  only. However, two or more button-holes may be provided. Alternatively or in addition, the strap  3301  may not be tube-like or sleeve-like but may have a flat single or laminate layer configuration. Here, the rigidiser arm  3302  may be positioned relative to the strap  3301  by the provision of retaining means including one or more loops, sleeve-like portions or pockets provided at the outer surface (e.g., the surface facing away from the patient in use) of strap  3301 . 
     In addition or alternatively, combinations of the different connection mechanisms described herein may be provided. For example, rigidiser arm  3302  may be fixed to the strap  3301  at a single point or localized area, as discussed above, adjacent, e.g. pocketed ends  3311 ,  3313  of strap  3301  while being held next to strap  3301  by provision of a loop or sleeve-like element provided at the outer surface of strap  3301 , e.g., in the area of the marks  3321   b ,  3323   b . In other words, the rigidiser arm  3302  may be connected to the strap  3301  by fixing it at one localized point or area only, while functioning as an additional guiding element to strap  3301 . Such guiding element functionality may be provided by a loop- or sheath-like portion or passage or a pocket of the strap  3301  into which or through which rigidiser arm  3302  extends based on the shape of the strap  3301  shown in  FIG.  66   . The strap  3301  may be tubular, but not necessarily cylindrical. This allows the longest stretch path possible for the strap  3301 . Alternatively, the rigidiser arm  3302  may be disposed unattached into one or more pockets (e.g., a single open-ended pocket of sheath of appreciable length supporting the rigidiser arm somewhere in the middle, or a pair of pockets, each supporting a respective end of the rigidiser arm), or a plurality of loops distributed along the length of the strap  3301 . Such guiding element functionality, whether attached at one end or not, allows substantially free movement or floating of the rigidiser arm  3302  relative to the strap  3301 . Such configuration would allow the same advantages and benefits as the configuration discussed above. Additionally, according to an example of the technology, the rigidiser arms  3302  do not stretch or flex in the same direction as the strap  3301 . Rather, the rigidiser arm  3302  may stretch or flex in a plane substantially perpendicular to its longitudinal axis. 
     In the shown and discussed examples, rigidiser arm  3302  does not extend beyond the end(s) of strap  3301 . However, according to alternative aspects, the rigidiser arm  3302  may be, e.g., fixed to strap  3301  at a point or area adjacent to the respective pocketed ends  3311 ,  3313  while extending beyond strap  3301 . In such a configuration, rigidiser arm  3302  may impart a shape, geometry, and/or rigidity to the strap  3301  and at the same time, provide structural means such, as a flexible joint  3305 , for connecting with a patient interface  3000 . This allows rigidiser arm  3302  to function both as rigidiser arm  3302  as well as a connector for connecting the strap  3301  and the positioning and stabilising structure  3300 , respectively, to the frame  3100 , plenum chamber  3200 , or seal-forming structure  3100 . 
       FIGS.  113  to  122    shows detailed views of the connection between the pocketed ends  3311 ,  3313  and the rigidiser arms  3302 .  FIGS.  113  and  114    show the pocketed ends  3311 ,  3313  around respective protruding ends  3306  of the rigidiser arms  3302 . The protruding ends  3306  are not visible in these views because they are covered by the pocketed ends  3311 ,  3313 . A straight section  3351  on an extension  3350  (discussed further below) of the rigidiser arm  3302  is shown with indicia  3358  on an outer surface  3355  of the extension  3350 . The indicia  3358  may be pad printed, a raised surface or an embossment to help the patient  1000  orient the device  3000  during use when in a darkened environment. The straight section  3351  of the extension  3350  may be seen extending outwardly from the button-hole  3303  of the respective pocketed end  3311 ,  3313 . The straight section  3351  is a part of the rigidiser arm  3302 , as shown in  FIGS.  47  to  60   , and the rigidiser arm  3302  facilitates the connection between the strap  3301  and the mask frame  3310 .  FIG.  114    shows a similar view to  FIG.  113   , however the outer surface  3355  of the straight section  3351  is without indicia. It should be understood that  FIG.  113    depicts the connection between one rigidiser arm  3302  and the respective pocketed end  3311  while  FIG.  114    depicts the connection between another rigidiser arm  3302  and the other respective pocketed end  3313 . By placing indicia  3358  on only one outer surface  3355 , the patient  1000  can use the sense of touch to determine the orientation of the device  3000  to aid in fitting in a darkened environment.  FIG.  114    also shows a flange  3359  that is visible through the button-hole  3303 . 
       FIG.  115    shows similar features to  FIG.  114    but is a more detailed view to better show the relationship between the flange  3359  and the pocketed end  3313 .  FIG.  116    also shows similar features to  FIG.  113    but is a more detailed view to better show the indicia  3358  and the button-hole  3303  in the pocketed end  3313 . 
       FIG.  117    shows a further detailed view of  FIG.  114    to better illustrate the button-hole  3303  at the pocketed end  3313 .  FIG.  118    shows a further detailed view of  FIG.  113    to better illustrate the button-hole  3303  at the pocketed end  3313 . 
       FIGS.  119  to  122    show similar features to those shown in  FIGS.  113  to  118   , however in these views the flange  3359  is pulled from the button-hole  3303  to better show its design.  FIGS.  119  and  122    show the rigidiser arm  3302  that includes the indicia  3358  on the outer surface  3355  extending from the button-hole  3303  of the pocketed end  3311 .  FIG.  122    should be understood to show a more detailed view of  FIG.  119   .  FIGS.  120  and  121    show the other rigidiser arm  3302  that may not include the indicia.  FIG.  121    should be understood to show a more detailed view of  FIG.  120   . 
       FIGS.  262 A and  262 B  show another example of the present technology where the strap  3301  includes an elastic tube  3301 . 1  to attach the strap to the rigidiser arm  3302 . According to this example, the strap  3301  may include the elastic tube  3301 . 1  fixed to an end of the strap.  FIG.  262 A  shows the strap  3301  and elastic tube  3301 . 1  detached from the rigidiser arm  3302  and a portion of the rigidiser arm is not shown for the sake of simplicity. To attach the strap  3301  to the rigidiser arm  3302 , the patient slides the elastic tube  3301 . 1  along the length of the rigidiser arm until it reaches a raised stop  3302 . 6  on the rigidiser arm. Although not shown in  FIGS.  262 A and  262 B , it should be understood that the length of the rigidiser arm  3302 , up to the point of the raised stop  3302 . 6 , is taken up inside of the strap  3301 . The raised stop  3302 . 6  prevents the patient from pushing the strap  3301  too far along the length of the rigidiser arm  3302  and may ensure that the strap is attached to the rigidiser arm at a desired position such that the strap retains the intended stretchable length. The shape, size, and material of the elastic tube  3301 . 1  may be chosen such that when the elastic tube reaches the raised stop  3302 . 6  a sufficient retention force due to friction is produced between the elastic tube and the rigidiser arm  3302 . In other words, the force of friction between the elastic tube  3301 . 1  and the rigidiser arm  3302  should be sufficiently high so that when the patient dons the patient interface  3000 , the force of tension in the strap  3301  is less than the force of friction retaining the elastic tube on the rigidiser arm, thereby preventing the elastic tube from being pulled off of the rigidiser arm. The elastic tube  3301 . 1  may be made from a material that has a relatively high coefficient of static friction with the material of the rigidiser arm  3302  to ensure that the strap  3301  will be retained on the rigidiser arm. Also, the material of the elastic tube  3301 . 1  should be stretchable so that it can deform as it is slid down the rigidiser arm  3302  to the raised stop  3302 . 6 . 
       FIG.  263    shows another example of the present technology where the rigidiser arm  3302  may be formed with a tab  3470  to retain the strap  3301  on the rigidiser arm with a hook and loop connection. The tab  3470  may be fixed to and/or formed integrally with the rigidiser arm  3302  and the tab may include hook material  3471 . Accordingly, at least a portion of the outer surface of the strap  3301  may be formed from a loop material, at least on a portion of its outer surface, to engage with the tab  3470  in a hook and loop connection. To attach the strap  3301  to the rigidiser arm  3302 , the patient may slide the strap along the length of the rigidiser arm and lift the tab  3470  to slide the strap thereunder and release the tab so that the loop material portion of the strap engages with the hook material  3471  on the strap. The size of the tab  3470  should be chosen so that a sufficient area of hook material  3471  engages the strap  3301  to produce a retention force that is sufficiently high to resist the tension force of the strap when donned by the patient. In this example, the entire strap  3301  may be manufactured to have loop material on its outer surface to save cost in manufacturing the strap. Accordingly, in such an example the loop material should be sufficiently soft so as to avoid irritation of the patient&#39;s skin. Also, it should be understood that the tab  3470  may include loop material rather than hook material, in which case the strap  3301  may have a portion of hook material to attach to the loop material of the tab. Additionally, it should be understood that the tab  3470  may be formed from an elastic material so that it may be pulled away from the rigidiser arm  3302  to attach the strap  3301  and then engage the strap when released with sufficient force to maintain the hook and loop connection. 
       FIGS.  264 A and  264 B  show another example of the present technology where the strap  3301  may include locks  3301 . 2  to engage with notches  3302 . 2  on the rigidiser arm  3302 . According to this example of the present technology, the locks  3301 . 2  may be positioned at the end of the strap  3301  and the strap may include elastic material at this end to urge the locks  3301 . 2  into engagement with the corresponding notches  3302 . 2  of the rigidiser arm  3302 . The strap  3301  should be sufficiently elastic at its ends in this example to ensure that the locks  3301 . 2  are held in the corresponding notches  3302 . 2  of the rigidiser arm  3302  with sufficient force to resist the force of tension of the strap when the patient interface  3000  is donned by the patient.  FIGS.  264 A and  264 B  show examples of the present technology with one notch  3302 . 2  on the top edge of the rigidiser arm  3302  and one notch on the bottom edge of the rigidiser arm along with corresponding locks  3301 . 2  on the strap  3301 , however, it should be understood that any number and/or position of corresponding locks and notches may be used so long as a sufficient force of retention is maintained. 
       FIG.  265    shows an example of the present technology where the strap  3301  includes a length of loop material  3301 . 3  and a piece of hook material  3301 . 4  at or near the end  3301 . 5  of the strap. The rigidiser arm  3302  according to this example of the present technology includes a first slot  3302 . 7  and a second slot  3302 . 8 . To attach the strap  3301  to the rigidiser arm  3302 , the strap is first threaded through the first slot  3302 . 7  and then looped back through the second slot  3302 . 8 . To fix the strap  3301  to the rigidiser arm  3302 , the hook material  3301 . 4  at the end  3301 . 5  of the strap is joined with the loop material  3301 . 3 . This example of the present technology may allow for some adjustability in the stretchable length of the strap  3301  based on where the hook material  3301 . 4  is attached to the loop material  3301 . 3 . Also, it should be understood that the location of the hook material  3301 . 4  and the loop material  3301 . 3  may be interchangeable. 
     The examples shown in  FIGS.  262 A to  265    include a strap  3301  that may be detached from the rigidiser arms  3302  and flipped such that either side of the strap may be used to contact the patient. This may be advantageous in that the strap  3301  may not be completely spent when the surface of one side of the strap is worn down. Rather, the patient may simply flip the strap  3301  such that the useful life of the strap may be increased. 
     Also, in any of the above examples where the strap  3301  of the positioning and stabilising structure  3300  is detachable, the detachable nature of the strap may be advantageous for the total lifecycle of the patient interface  3000 . For example, the strap  3301  may have a shorter useful life than the frame  3310  and short tube  4180  assembly such that expiration of the strap does not necessitate replacement of the entire patient interface  3000 . In other words, the strap  3301  can replaced once expired and a new strap can be used with the remainder of the patient interface  3000  that has not expired. 
     Permanent Attachment Alternative 
       FIGS.  266  to  270    show alternative examples of the present technology where the strap  3301  may be permanently attached to the rigidiser arms  3302 , i.e., the strap cannot be removed from the rigidiser arms by the patient. Permanently attaching the strap  3301  to the rigidiser arms  3302  may be advantageous in that it is unnecessary for the patient to thread the strap onto the rigidiser arms and it is also not possible for the strap to come undone from the rigidiser arms. 
       FIG.  266    shows an example of the present technology where the strap  3301  is permanently fixed to the rigidiser arm  3302  at attachment points  3304 . According to this example, the attachment points  3304  may be formed by ultrasonic welding of the strap  3301  to the rigidiser arm  3302 . While two attachment points  3304  are shown on the surface of the rigidiser arm  3302  that faces away from the patient in use, it should be understood that the number, size, shape, and/or location of the attachment point(s)  3304  may be varied so long as the desired stretchable length of the strap  3301  relative to the rigidiser arm  3302  is maintained. 
       FIG.  267    shows an example of the present technology that is similar to the example shown in  FIG.  266   . However, the example shown in  FIG.  267    includes attachment points  3304  formed by heat staking rather than ultrasonic welding. Also, it should be understood that the size, shape, number, and/or location of the attachment point(s)  3304  may be varied so long as the desired stretchable length of the strap  3301  relative to the rigidiser arm  3302  is maintained. 
       FIG.  268    shows a further example of the present technology that is similar to the example shown in  FIG.  266   . However, the example shown in  FIG.  268    includes attachment points  3304  formed by stitching. Also, it should be understood that the size, shape, number, and/or location of the attachment point(s)  3304  may be varied so long as the desired stretchable length of the strap  3301  relative to the rigidiser arm  3302  is maintained. 
       FIG.  269    shows another example of the present technology where the attachment point  3304  is fixed to the rigidiser arm  3302  in a hinged arrangement and permanently fixes the strap  3301  to the rigidiser arm. For example, the attachment point  3304  may pierce the fabric of the strap  3301  to form a permanent attachment. 
       FIG.  270    shows another example of the present technology where the permanent attachment of the strap  3301  to the rigidiser arm  3302  uses barbs at the attachment point  3304 . The barbs of the attachment point  3304  may be formed integrally with the rigidiser arm  3302  and may be oriented such that when the strap  3301  is first slid onto the rigidiser arm, the relatively soft fabric of the strap is gripped and permanently attached by the barbs. In other words, the barbs of the attachment point  3304  may be oriented to point in the opposite direction of the force of tension of the strap  3301  when the patient interface  3000  is donned by the patient. 
     Stretching of Straps Relative to Rigidiser Arms 
     As can be seen in the example shown in  FIG.  68   , two rigidiser arms  3302  are inserted into side strap portions  3315 ,  3316  of the strap  3301  of the positioning and stabilising structure  3300 , the rigidiser arm  3302  is held in place by the surrounding strap  3301  while at the same time the sleeve-like configuration of strap  3301  allows at least a portion of the strap  3301  to stretch or move relative to the rigidiser arm  3302 . Preferably, this stretchable portion is a substantial portion because only at the anchor point is the strap  3301  secured to the rigidiser arm  3302 . In some examples, a limitation on the movement of the rigidiser arm  3302  is generally imposed when one of the ends  3319   a  or  3319   b  of the rigidiser arm  3302  moves towards and abuts against a respective pocketed end  3311  of the strap  3301 , as in  FIG.  69   . For example, when the positioning and stabilising structure  3300  is not on the patient&#39;s head and the straps  3301  are loose, when the inserted rigidiser arm  3302  moves too far towards the back strap portions  3317   a ,  3317   b , its end  3319   b  may enter the open end of one of these back strap portions  3317   a ,  3317   b . As the width of the back strap portions  3317   a ,  3317   b  is smaller than that of the rigidiser arm  3302 , the end  3319   b  of the rigidiser arm  3302  abuts against the respective back strap portion  3317   a ,  3317   b , which restricts its further movement in this direction. 
     The attachment of the strap  3301  to the rigidiser arm  3302  described in the preceding section may also affect the size of head that the positioning and stabilising structure  3300  may accommodate. In other words, by providing a greater length of strap  3301  along the rigidiser arm  3302  it may be possible to increase the total stretchable length of the positioning and stabilising structure  3300  such that even larger circumference heads may be accommodated without needing to increase the stretchability of the strap  3301 . Furthermore, it may be possible to vary, along the length of the rigidiser arm  3302 , where the strap  3301  is connected. This would allow for an even greater range of head sizes and circumferences to be accommodated without the need to alter the stretchability of the strap  3301 . 
     The length of the strap  3301  is from about 400 mm to 700 mm. The length of the strap  3301  may be about 490 mm. The strap  3301  may provide a comfortable level of headgear tension for most head sizes. There may be two lengths or sizes of straps which are gender specific, the one for the male population being longer than the female version. Preferably, there may be two sizes/lengths of the strap  3301  for each gender. A comfortable level of headgear tension is from about 2 to about 5 Newtons. A comfortable level of headgear tension is from about 2.2 Newtons to about 4.7 Newtons. When the strap  3301  is stretched from 490 mm to 526 mm for a small circumference head of a patient  1000 , the headgear tension as measured using an Instron machine is 2 Newtons. When the strap  3301  is stretched from 490 mm to 662 mm for a large circumference head of a patient, the headgear tension as measured using an Instron machine is 4.4 Newtons. For the measurement, the button-holes  3303 ,  3304  of the strap  3301  are attached onto clamping fixtures. A tensile testing machine with a 100 Newtons load cell is used. The strap  3301  is extended and held at predetermined extension points (e.g. 90.5 mm, 73 mm and 108 mm) for one minute, and the force value (in Newtons) is recorded for each extension point. Such measurement does not consider any friction of the material of the strap  3301  against the patient&#39;s face or hair. 
     The length of a split region  3326  defined between the two back strap portions  3317   a ,  3317   b  is from about 180 mm to about 220 mm. The length of the split region  3326  may be 200 mm. If the length of the split region  3326  is not long enough, the two back strap portions  3317   a ,  3317   b  will be unable to cup the back of the patient&#39;s head and therefore unable to maintain their position during therapy and the headgear tension will not remain set to the patient&#39;s preference. If the length of the split region  3326  is too long, the two back strap portions  3317   a ,  3317   b  will separate in front of the user&#39;s ears and be uncomfortable as they pass over the ears rather than above/around it and also it reduces the maximum angle range for the two back strap portions  3317   a ,  3317   b  with respect to each other. 
     In the neutral and unstretched condition of the strap  3301 , the two back strap portions  3317   a ,  3317   b  have an angle θ from each other at about 0° to about 10°. After donning the patient interface  3000 , the two back strap portions  3317   a ,  3317   b  may be split from each other such that the angle θ may be up to about 180°. This allows a maximum angular range of 180° which in turn gives a large range for the reduction of headgear tension through incrementally spreading apart the two back strap portion  3317   a ,  3317   b . The angular range may be narrowed to a default angle of 10° to a maximum angle of 120°. The patient may use one or both hands to move the two back strap portion  3317   a ,  3317   b  now under tension on the back of their head, apart or together. By moving the two back strap portion  3317   a ,  3317   b  further apart from each other, the split region  3326  enlarges, leading to a reduction in headgear tension from the unsplit range of 2.5 to 5 Newtons. The headgear tension may be reduced from about 30% to about 50% according to one example, or to about 40% in another example, as measured by a load cell. In other words, for a small circumference head of a patient, the headgear tension may be reduced from 2 Newtons to 1.2 Newtons by enlarging the separation between the two back strap portions  3317   a ,  3317   b . For a large circumference head of a patient, the headgear tension may be reduced from 4.4 Newtons to 2.64 Newtons by enlarging the separation between the two back strap portions  3317   a ,  3317   b.    
     The rigidiser arm  3302  may thus be allowed to move generally unrestrictedly along the length of the strap  3301 , attached to the strap  3301 , or may be adjacent one of its ends. 
     The discussed configurations allow, as shown in  FIG.  70   , the strap  3301 , and thus, the positioning and stabilising structure  3300  to stretch and expand in length. Such elongation is not limited to those portions of the strap  3301  that are not in contact with or parallel to the rigidiser arm  3302  but also, elongation, particularly elastic elongation of the strap  3301 , is achieved in the area of rigidiser arm  3302 . This can easily be derived from comparison of the length of the rigidiser arm  3302  in  FIGS.  68  and  70    (which remains the same although the strap  3301  is stretched) with marks  3321   a - d ,  3323   a - e  visualizing the length of the strap  3301  with regard to the length of the rigidiser arm  3302 . It is easily derivable by comparison of  FIGS.  68  and  70    that the rigidiser arms  3302  extend along marks  3321   a  to  3321   c  and  3323   a  to  3323   d , respectively in  FIG.  68    in the un-stretched state. Contrary thereto, in the stretched state according to  FIG.  70   , rigidiser arms  3302  extend along marks  3321   a  to  3321   b  and  3323   a  to  3323   c , only. Therefrom, it becomes clear that strap  3301  is stretched also in and along the area where rigidiser arms  3302  are contained in strap  3301 . The rigidiser arms  3302  remain un-stretched however during stretching of the strap  3301 . 
     As will be appreciated, positioning and stabilising structure  3300  may comprise one or more rigidiser arms  3302 . While the above discussion concentrates on the relationship of a rigidiser arm  3302  with a strap  3301 , it is to be noted that the example shown in  FIGS.  68  to  70    comprises two rigidiser arms  3302 , one being provided in each respective side strap portion  3315 ,  3316  of strap  3301 . The above comments, although eventually referring to one rigidiser arm  3302 , thus equally apply to two or more rigidiser arms  3302  connected to a mask frame  3310 . 
     One possibly advantageous attribute of allowing the strap  3301  to stretch relative to the rigidiser arm  3302  as heretofore described may be that the patient interface  3000 , along with the positioning and stabilising structure  3300 , may be donned and doffed by the patient  1000  without the need to disconnect any straps or other connection features. This may be helpful to a patient  1000  that is using the device  3000  in a dark bedroom prior to or following sleep, in that the patient does not need to be able to see to connect or disconnect various components to attach or remove the patient interface  3000 . Rather, the patient  1000  may only need to simply pull on or off the patient interface  3000  and positioning and stabilising structure  3300 , and in the case of donning it may also be necessary to position the seal-forming structure  3100 . However, this may all be accomplished by feel, sight being unnecessary. 
     It may however remain advantageous to allow disconnection of the plenum chamber  3200  or seal-forming structure  3100  from the positioning and stabilising structure  3300 . For example, to clean the plenum chamber  3200  or seal-forming structure  3100  it may be desirable to wash it while not getting the positioning and stabilising structure  3300  wet. This may be facilitated by allowing these components to disconnect for such a purpose. 
     Rigidiser Arms and Mask Frame 
       FIGS.  47  to  60    show rigidiser arms  3302  and a mask frame  3310  according to a further example of the present technology. 
       FIGS.  47  to  49  and  54    show cross-sectional views of a rigidiser arm  3302  and a mask frame  3310  and the connection therebetween, according to an example of the present technology. Near a sharp bend  3307  of the rigidiser arm  3302  an extension  3350  is connected by a joint  3356 . Also near the sharp bend  3307  is a protruding end  3306  of the rigidiser arm  3302  that may retain a pocketed end of a side strap portion  3316  of the positioning and stabilising structure  3300 . In these views the mask frame  3310  can be seen formed around a hook  3353  and an enclosable section  3354  of the extension  3350 . An opening  3335  may also be formed in the mask frame  3310  near where the mask frame  3310  surrounds the enclosable section  3354 . The opening  3335  may be formed as a result of the overmolding process by which the mask frame  3310  is formed and secured around the enclosable section  3354  of the rigidiser arm  3302 . The rigidiser arm  3302  according to this example may be formed from Hytrel® and the mask frame  3310  may be formed from polypropylene (PP). Hytrel® is desirable for forming the rigidiser arms  3302  because this material is resistant to creep. Since these materials cannot be integrally bonded the mask frame  3310  may be overmolded to the rigidiser arm  3302  in this example to form a secure connection. It should also be noted that in this example the extension  3350  and the rigidiser arm  3302  may be molded as one piece. The mask frame  3310  may be connected to the rigidiser arms  3302  at respective extensions  3350  located opposite distal free ends  3302 . 1 . The extension  3350  may comprise a straight section  3351  joined to a bend  3352  joined to a hook  3353 . The hook  3353  and a portion of the bend  3352  may form the enclosable section  3354 . 
     It should be understood that the joint  3356  that connects extension  3350  to the rigidiser arm  3302  may provide a targeted point of flexibility and the joint may be shaped and formed to allow flexing in a desired direction and degree. Thus, once the patient interface  3000  is donned and the rigidiser arms  3302  are stressed by tension from straps of the positioning and stabilising structure  3300  the rigidiser arms  3302  may flex at the joints  3356  to allow them to retain a face framing shape while helping to retain the mask frame  3310  in a desired position relative to the patient&#39;s face. 
       FIGS.  50  and  51    show perspective and detailed perspective views, respectively, of rigidiser arms  3302  connected to a mask frame  3310 , according to an example of the present technology.  FIG.  51    further shows the enclosable section  3354  in dashed lines and overmolded by the mask frame  3310  to secure the mask frame to the end of the rigidiser arm  3302 . The opening  3335  can be seen, as in  FIGS.  47  to  49   , forming a passage completely through the mask frame  3310  and the hook  3353  of the rigidiser arm  3302 . 
       FIGS.  52  and  53    show top and detailed top views, respectively, of a mask frame  3310  connected to rigidiser arms  3302 , according to an example of the present technology. In  FIG.  52    the dimension L indicates the length of the rigidiser arm  3302  in the direction shown. Preferably, the nominal length L of a rigidiser arm  3302  is 114 mm. These views show particularly well how the joint  3356  may connect the extension  3350  to the rigidiser arm  3302  between the protruding end  3306  and the sharp bend  3307 . 
       FIGS.  55  to  57    show side, front, and perspective views, respectively, of rigidiser arms  3302  and a mask frame  3310 , according to an example of the present technology. In  FIG.  55   , the dimension H indicates the height of the rigidiser arm  3302  in the direction shown. Preferably, the nominal height H of a rigidiser arm  3302  is 33 mm. The rigidiser arm  3302  and the extension  3350  may be formed as one piece and then connected to the mask frame  3310  by overmolding the mask frame  3310  to the enclosable section  3354  of the extension  3350  of the rigidiser arm  3302 . The extension  3350  accommodates nose droop by bending in a pivoting manner or vertical rotates relative to the rigidiser arm  3302 . Since the extension  3350  has a smaller height, has less material than the remainder of the rigidiser arm  3302  and is decoupled from the remainder of the rigidiser arm  3302  by the sharp bend  3307 , bending of the extension  3350  is localised and occurs before the remainder of the rigidiser arm  3302  starts to bend. This reduces the likelihood of disruption of sealing forces. 
       FIGS.  58  and  59    show partially exploded and detailed partially exploded views, respectively, of rigidiser arms  3302  and a mask frame  3310 , according to an example of the present technology. The hook  3353  and the enclosable section  3354  of the extension  3350  can be seen separated from the mask frame  3310 . The shape of the hook  3353  and the enclosable section  3354  may be seen in these views and it should be understood that these portions are formed to ensure a stronger mechanical interlock with the mask frame  3310  when the mask frame  3310  is overmolded. Specifically, these views show that the enclosable section  3354  may be formed with flared ends at the hook  3353  to provide surfaces for retention to the mask frame  3310 . In another example of the technology, the enclosable section  3354  may include an opening for restraining the rigidiser arm  3302  within the mold tool(s) during overmolding of the mask frame  3310 . A mold tool may be inserted through this opening to stabilize the rigidiser arm  3302  as the mask frame  3310  is overmolded around the rigidiser. This may be advantageous because the pressures of overmolding may cause the rigidiser arm  3302  to shift during the molding process such that a less than ideal mechanical interlock with the mask frame  3310  would be formed. 
       FIG.  60    shows a perspective view of a rigidiser arm  3302  according to an example of the present technology. It shows the rigidiser arm  3302  prior to permanent connection with the mask frame  3310 . As discussed immediately above, the rigidiser arm  3302  may include a hook  3353  and an enclosable section  3354  to allow for connection to the mask frame  3310  via mechanical interlock. This permanently connects the rigidiser arm  3302  to the frame  3310 . By having the rigidiser arm  3302  and the frame  3310  permanently connected together, it means that there are less detachable parts and reduced likelihood of losing a part during assembly/disassembly of the patient interface  3000  when cleaning. 
     Increasing Stability Between the Frame and Rigidiser Arms 
     According to certain examples of the present technology, it may be desirable to join the frame  3310  and the rigidiser arms  3302  in a manner than enhances the stability of the patient interface  3000 . 
       FIG.  260 A  shows an example of the present technology wherein the rigidiser arm  3302  is molded to the frame  3310 . The frame  3310  and the rigidiser arm  3302  may be formed in one piece. This example does not include the extension  3350  provided in other examples to provide the desired amount of flexural strength at the juncture between the frame  3310  and the rigidiser arm  3302 . Rather, extension arms  3302 . 3  are molded to join the rigidiser arm  3302  to the frame  3310 . As part of the molding process, a void  3302 . 4  may be formed between the extension arms  3302 . 3  to remove unnecessary material. It should be understood that by spreading the upper and lower extension arms  3302 . 3  apart further, the moment of inertia where the extension arms join to the frame may be increased about the axis X-X shown in  FIG.  260 A . The formula for the moment of inertia of this joint about X-X may be simplified to 
     
       
         
           
             I 
             = 
             
               
                 
                   bh 
                   3 
                 
                 12 
               
               . 
             
           
         
       
     
     Thus, an increase in h, i.e., the space between the upper and lower extension arms  3302 . 1 , would yield a significant increase in the moment of inertia, I, about X-X relative to increasing b, i.e., the thickness of the extension arms. Moreover, by optimizing the geometry of the rigidiser arm the rigidiser arms  3302  and/or the extension arms  3302 . 1  may be made thinner. 
       FIG.  260 B  shows another example of the present technology where the rigidiser arm  3302  may be joined to the frame  3310  by rods  3302 . 5 . The rods  3302 . 5  may be metal or another similar material having comparable stiffness. Additionally, the rigidiser arms  3302  of this example may be formed from a relatively rigid material such as Nylon. 
       FIG.  261 A  shows another example of the present technology wherein it may be desirable to increase the stability of the rigidiser arms  3302  and extensions  3350 . A pair of rigidiser arm ribs  3460  may be provided to the rigidiser arm  3302  at the sharp bend  3307  to increase rigidity. A pair of extension ribs  3461  may be provided at the bend  3352  of the extension to increase rigidity. The sharp bend  3307  and the bend  3352  may be susceptible to undesirable deflection when the patient interface  3000  is donned by the patient. Thus, these ribs may prevent excessive bending of the rigidiser arm  3302  and/or the extension  3350 . 
       FIG.  261 B  shows another example of the present technology where it may be desirable to increase the stability of the extension  3350 . In this example, a longitudinal rib  3462  is provided along a portion of the extension  3350  in a longitudinal direction. The longitudinal rib  3462  may extend through the bend  3352  to the straight section  3351 . The longitudinal rib  3462  may increase the rigidity of the extension  3350  to prevent excessive bending. 
     Positioning and Stabilising Structure on a Patient 
       FIGS.  71  to  73    show an example of the present technology. Here, the positioning and stabilising structure  3300  comprises a strap  3301  with side strap portions  3315 ,  3316  and a back strap portion  3317  comprising two back strap portions  3317   a ,  3317   b  running in parallel along the back of a patient&#39;s head. The positioning and stabilising structure  3300  comprises two rigidiser arms (not shown), each contained in a respective side strap portion  3315 ,  3316  of the sleeve- or tube-like strap  3301 . Rigidiser arms  3302  impart a predetermined shape or desired shape and/or rigidity to the strap  3301 , and thus, the positioning and stabilising structure  3300 . For example, the side strap portions  3315 ,  3316  of the strap  3301  have a certain curvature for following a desired contour around a patient&#39;s face (see curvature at reference numeral  3323  in  FIGS.  52 ,  54 ,  58 , and  60   ), which is achieved by the provision of respectively shaped rigidiser arm  3302 . In the example shown, the positioning and stabilising structure  3300  is connected to the frame  3310 , plenum chamber  3200  or seal-forming structure  3100  for providing breathable gas such as air, eventually pressurized breathable gas, to a patient&#39;s airways. In the shown example, such breathable gas is provided via the hose or tube  4180  connected to patient interface  3000 . The tube  4180  may be connected at its other end (not shown) to a source of breathable gas, such as a blower or ventilator for providing pressurized breathable gas. The patient interface  3000  may comprise a frame portion or frame  3310  for imparting structural integrity to the patient interface  3000  and/or for connecting to the positioning and stabilising structure  3300 . The positioning and stabilising structure  3300  may be connected to the frame  3310 , plenum chamber  3200  or seal-forming structure  3100  via a separate connector means (not shown) provided on strap  3301  and/or rigidiser arm  3302 . 
       FIGS.  74  to  77    show similar features to those shown in  FIGS.  71  to  73   , however the examples shown in  FIGS.  74  to  76  and  77    depict a different connection between the positioning and stabilising structure  3300  and the mask frame  3310 . At each end of the side strap portions  3315 ,  3316  there is a pocketed end  3311 ,  3313  as shown in  FIGS.  65  and  81   . These pocketed ends  3311 ,  3313  are retained on the rigidiser arms  3302  (not visible in these views because they are within the side strap portions  3315 ,  3316 ) by the protruding end  3306  of respective rigidiser arms shown, for example, in  FIGS.  47  to  60   . Although not visible in  FIGS.  74  to  77   , it should be understood that, in this example, end welds  3311 . 1 ,  3313  depicted in  FIG.  81    serve to close the pocketed ends  3311 ,  3313  so that they may be retained against the protruding ends  3306 . The rigidiser arms  3302  are then permanently and mechanically secured to the mask frame  3310  by overmolding, for example, as described with reference to  FIGS.  47  to  60   . 
     Attachment of Rigidiser Arms to Patient Interface 
     According to further examples of the present technology, the rigidiser arms  3302  may be detachable. By making the rigidiser arms detachable from the patient interface  3000  the rigidiser arms  3302  may be subject to less distortion during transport and storage. When the rigidiser arms  3302  are detachable, the patient interface  3000  may be packed more compactly and in a manner that adequately supports each individual component. Also, by making the rigidiser arms  3302  separable it is possible to separate them for cleaning. It should be understood that in some examples the extensions  3350  may be detached from the frame  3310 . In other examples the rigidiser arms  3302  may be detached from the extensions  3350 , in which case the extensions may be permanently attached to the frame  3310 . A further advantage of detachable rigidiser arms  3302  may be that the attachment mechanism can be designed to produce an audible click that is a reassuring indication to the patient that the components have been effectively secured. Such an audible click may be facilitated by a hard-to-hard connection between the rigidiser arms  3302  and the frame  3310 , for example. A hard-to-hard connection may be beneficial for patients that struggle with fine motor skills because it may allow them to more easily assembly the patient interface  3000  and be confident that they have done so. Also, detachable rigidiser arms  3302  may be beneficial for the patient in that he or she may customize the patient interface  3000  because of the interchangeability of parts. For example, the patient interface  3000  may be sold with a number of rigidiser arm  3302  sets that have different curve profiles, shapes, lengths, and/or stiffnesses, from which the patient may choose the most suitable set based on facial geometry and comfort. This in turn may provide a better fit and greater comfort, which may improve patient compliance. Also, the rigidiser arm  3302  sets may be provided in different colors such that the patient is provided with a variety of options aesthetically. 
       FIGS.  248 A and  248 B  show an example of a rigidiser arm  3302  detached from and attached to a patient interface  3000  at the extension  3350 . On the protruding end  3306  of the rigidiser arm  3302 , a projection  3380  may be provided with locking wings  3381  and supported by a shaft (not shown). On the straight section  3351  of the extension  3350 , an opening  3382  with notches  3383  may be provided. Stops  3384  may also be provided on the straight section  3351  of the extension  3350 . The opening  3382  and notches  3383  may be sized and shaped correspondingly to the projection  3380  and the wings  3381 . To assemble the rigidiser arm  3302  to the extension  3350 , the projection  3380  and the wings  3381  are extended through the corresponding opening  3382  and notches  3383  and then rotated until the wings abut against their respective stops  3384 . Accordingly, the length of the shaft should be sized to be slightly larger than the width of the straight section  3351  of the extension  3350  to minimize play between the rigidiser arm  3302  and the extension  3350  once attached. It should be understood that the rigidiser arm  3302  may be secured by rotation in only one direction. This may be accomplished by positioning the stops  3384  on respective sides of the opening  3382  so that, as shown for example in  FIG.  248 B , the rigidiser arm  3302  is secured by clockwise rotation. Also, it should be understood that to prevent misassembly of the rigidiser arms  3302 , i.e., where the right side rigidiser arm may be attached to the left side extension and vice versa, the corresponding projection-wing and opening-notch sets may be differently sized. Thus, the patient would only be able to securely attach the right side rigidiser arm  3302  to the right side extension  3350  and the left side rigidiser arm to the left side extension. 
       FIGS.  249 A and  249 B  show another example of the present technology where the rigidiser arms  3302  may be detachable. In this example, the extension  3350  may be provided with a pair of pins  3385  extending therefrom. The pins  3385  may each comprise a head on a shaft, the shaft being fixed to the extension  3350 . The head of each pin  3385  may be larger in diameter than the shaft of each pin to allow for attachment to sockets  3386  formed in the protruding end  3306  of the rigidiser arm  3302 . The sockets  3386  may include slits to allow for deflection of the material of the protruding end  3306  so that the heads of the pins  3385  can pass through the respective sockets. Accordingly, the length of the shafts of the pins  3385  should be sized to be slightly larger than the width of the protruding end  3306  to minimize play once the rigidiser arm  3302  is attached. Also, the pins  3385  and corresponding sockets  3386  may be spaced or sized differently to prevent misassembly of the rigidiser arms  3302 . For example, the spacing and/or positioning of the pins  3385  and corresponding sockets  3386  of the right side rigidiser arm  3302  and extension  3350  may be different from the left side so that the patient cannot attach the left side rigidiser arm to the right side extension and vice versa. In another example, the pins  3385  and sockets  3386  of the left side rigidiser arm  3302  and extension  3350  may be sized differently from the pins and sockets of the right side rigidiser arm and extension so that the patient cannot attach the left side rigidiser arm to the right side extension and vice versa. 
       FIGS.  250 A to  250 C  show another example of a rigidiser arm  3302  that is detachable according to the present technology. In this example, the rigidiser arm  3302  includes a projection  3393  with an arm  3394  to secure the rigidiser arm to the extension  3350 . The arm  3394  and the projection  3393  may extend from a shaft  3395  on the rigidiser arm  3302  and the arm, the projection, and the shaft may be formed in one piece with the rigidiser arm  3302 . Accordingly, the extension  3350  is provided with a slot  3392  through which the arm  3394  and the projection  3393  are passed during attachment. The extension  3350  is also formed with a shaft receiver  3390  and an arm receiver  3391  to respectively receive the shaft  3395  and the arm  3394 . To attach the rigidiser arm  3302  to the extension  3350 , the shaft  3395 , the projection  3393 , and the arm  3394  are passed through the slot  3392  and the shaft and the projection are pulled into engagement with the shaft receiver  3390  and the arm receiver  3391 , respectively. The arm receiver  3391  may be narrower than the shaft  3395  and the arm  3394  to ensure that when the arm is engaged in the arm receiver a secure friction-fit results. To detach the rigidiser arm  3302  from the extension  3350 , the patient would slide the rigidiser arm  3302  in the opposite direction of attachment. It should also be understood that the diameter of the projection  3393  may be greater than the diameter of shaft receiver  3390  to prevent disassembly. To prevent misassembly, the arm  3394  and the projection  3393  of the right side rigidiser arm  3302  may be sized and/or shaped to only fit in the arm receiver  3391  and shaft receiver  3390  of the right side extension  3350  and the arm and the projection of the left side rigidiser arm may be sized and/or shaped to only fit in the arm receiver and shaft receiver of the left side extension. 
       FIGS.  251 A and  251 B  show another example of a rigidiser arm  3302  that may be detachable. According to this example, the extension  3350  may be formed in one piece with the rigidiser arm  3302 . The extension  3350  may include a flared end  3387  that attaches to a receiver  3388  on the frame  3310 . The flared end  3387  may be slid into a slot  3389  in the receiver  3388  to attach the extension  3350  and the rigidiser arm  3302  and the engagement may comprise a press-fit. The receiver  3388  may be a separate component from the frame  3310  that is attached thereto, or the receiver may be formed integrally with the frame. The right side flared end  3387  and slot  3389  may be sized and/or shaped differently from the left side flared end and slot to prevent misassembly. 
       FIGS.  252 A to  252 C  show another example of a rigidiser arm  3302  that may be detachable. According to this example, the extension  3350  may be formed in one piece with the rigidiser arm  3302 . The extension  3350  may be formed to provide a snap-fit engagement with a receiver  3310 . 1 . The receiver  3310 . 1  may be a separate component from the frame  3310  that is attached thereto, or the receiver may be formed integrally with the frame. The receiver  3310 . 1  may include a pocket  3310 . 2  and a recess  3310 . 3  to receive the extension  3350  for attachment of the rigidiser arm  3302 . The extension  3350  includes a bend  3396  that facilitates the snap-fit engagement. The extension  3350  may be made from an elastic material and sized such that when the extension is placed into the receiver  3310 . 1 , the extension is compressed by reduction of the angle of the bend  3396 . This compression of the extension  3350  forces a protrusion  3397  into the recess  3310 . 3  when the bend  3396  is forced into the pocket  3310 . 2 . A tab  3398  may also be provided to facilitate disengagement. The patient may press the tab  3398  and compress the bend  3396  further to release the protrusion  3397  from the recess  3310 . 3  to detach the rigidiser arm  3302 . Also, the right side extension  3350  and the corresponding receiver  3310 . 1  may be sized and/or shaped differently from the left side extension and corresponding receiver to prevent misassembly. 
       FIGS.  253 A to  253 C  show another example of a rigidiser arm  3302  that may be detachable. According to this example, the extension  3350  may be formed in one piece with the rigidiser arm  3302 . The extension  3350  may be formed to provide a snap-fit engagement with a receiver  3310 . 1 . In this example, the extension  3350  may be held by the receiver  3310 . 1  with a friction fit. The receiver  3310 . 1  may be a separate component from the frame  3310  that is attached thereto, or the receiver may be formed integrally with the frame. In this example, a column  3399  may be provided near an end  3350 . 1  of the extension  3350 . To attach the extension  3350 , the column  3399  is inserted into the pocket  3310 . 2  of the receiver  3310 . 1 . The column  3399  may be circular in cross-sectional profile to engage with complementarily shaped indentations  3310 . 4  of the pocket  3310 . 2 . Cross-sectional profiles of the column  3399  other than circular are envisioned as well, such as square, rectangular, triangular, oval, etc. As these respective surfaces may be curved in this example, an end receiver  3310 . 5  may also be provided in the pocket  3310 . 2  to receive the end  3350 . 1  of the extension  3350 . The engagement of the end  3350 . 1  of the extension  3350  with the end receiver  3310 . 5  may prevent undesirable rotation of the extension  3350  and the rigidiser arm  3302  about the longitudinal axis of the column  3399 . Accordingly, this may ensure that the only motion of the rigidiser arm  3302  is due to deflection resulting from the deformable nature of the rigidiser arm  3302  and the extension  3350 , and not because of play in the engagement between the extension and the receiver  3310 . 1 . Accordingly, the right side extension  3350  and corresponding receiver  3310 . 1  may be sized and/or shaped differently from the left side extension and receiver to prevent misassembly. 
       FIGS.  254 A and  254 B  show another example of a rigidiser arm  3302  that may be detachable. This example may not include an extension  3350  formed with the rigidiser arm  3302 . Rather, the rigidiser arm  3302  may be formed with a first bend  3340 , a first straight section  3341 , a second bend  3342 , a second straight section  3343 , and a locking end  3344  formed at the end of the second straight section  3343 . At each side of the frame  3310 , a slot  3345  may be provided through which each rigidiser arm  3302  may be threaded for attachment to the frame. Each slot  3345  may be sized and shaped to allow the respective rigidiser arm  3302  to pass therethrough but each slot may also be smaller than the respective locking end  3344  to prevent the rigidiser arms from being pulled through. To prevent misassembly, the right side rigidiser arm  3302  and corresponding slot  3345  may be shaped and/or sized differently from the left side rigidiser arm and slot. It should also be understood that the portions of the rigidiser arm  3302  referred to above as the first straight section  3341  and the second straight section  3343  need not be straight and these sections may instead be curved as necessary to provide the desired shape/profile. Additionally, the rigidiser arm  3302  may have other curves and/or bends as desired, so long as the rigidiser arm can be threaded through the slot. 
       FIGS.  255 A and  255 B  show another example of a rigidiser arm  3302  that may be detachable. According to this example, the extension  3350  may be formed in one piece with the rigidiser arm  3302 . This example includes a pin  3385  with a head supported on the extension  3350  by a shaft. The head of the pin  3385  may be larger in diameter than the shaft. A socket  3386  may be formed integrally on each side of the frame  3310  for a snap-fit engagement with the respective pin  3385 . To prevent misassembly, the pin  3385  of the right side rigidiser arm  3302  and the corresponding socket  3386  may be sized and/or shaped differently from the pin and socket of the left side. 
       FIGS.  256 A to  256 C  show another example of a rigidiser arm  3302  that may be detachable. According to this example, the extension  3350  may be formed in one piece with the rigidiser arm  3302 . A receiver  3410  and a first magnet  3412  may be provided to the frame  3310 . A second magnet  3413  may be provided to the extension  3350  to secure the rigidiser arm  3302  to the frame  3310 . Accordingly, the respective poles of the first magnet  3412  and the second magnet  3413  may be oriented so that the first magnet and the second magnet are attracted to one another. A post  3411  may also be provided to extension  3350  proximal to the second magnet  3413  to engage with the receiver  3410  and ensure that the extension is properly positioned in the receiver. It should also be understood that the right side post  3411  and receiver  3410  may be shaped and/or sized differently from the left side post and receiver to prevent misassembly. To prevent misassembly, the poles of the right side first magnet  3412  and second magnet  3413  may be oriented opposite to the poles of the left side first magnet and second magnet such that magnetic attraction only occurs when the respective right and left side magnets are engaged and should the patient try to place the left side rigidiser arm  3302  into the right side receiver  3410 , or vice versa, magnetic repulsion will prevent engagement. 
       FIGS.  257 A and  257 B  another example of a rigidiser arm  3302  that may be detachable. The frame  3310  may include a first L-shaped section  3420  on each side and a second L-shaped section  3423  may be formed on each rigidiser arm  3302 . To attach the frame  3310  to the rigidiser arm  3302 , the first L-shaped section  3420  is brought into engagement with the second L-shaped section  3423  by moving the L-shaped sections toward one another in opposite vertical directions. The first L-shaped section  3420  and the second L-shaped section  3423  are then rotated against one another and secured in position. A second overlapping portion  3424  may engage with a first recessed portion  3421  and a first overlapping portion  3422  may engage with a second recessed portion  3425 . A peg  3426  may be provided to the first recessed portion  3421  and the second recessed portion  3425 . To secure the first L-shaped section  3420  and the second L-shaped section  3423 , each peg  3426  may engage with a hole  3427  provided to the first overlapping portion  3422  and the second overlapping portion  3424 . The holes  3427  in these examples are shown in dashed lines to indicate that they do not extend completely through the first overlapping portion  3422  and the second overlapping portion  3424 , but it should be understood that according to an alternative example that the holes could extend the completely through. It should also be understood that the engagement between the respective pegs  3426  and holes  3427  may include a press- or friction-fit to ensure a secure connection. In a further alternative example, the pegs  3426  may comprise a barb at the end of a shaft and each corresponding hole  3427  may extend completely through the first overlapping portion  3422  and the second overlapping portion  3424  such that when engaged the barb of each peg locks into the respective hole. Also, it should be understood that the pegs  3426  could be provided to the first overlapping portion  3422  and the second overlapping portion  3424  and the holes  3427  could be provided to the first recessed portion  3421  and the second recessed portion  3425  in an alternative example. 
       FIGS.  258 A and  258 B  show another example of a rigidiser arm  3302  that may be detachable. According to this example, the extension  3350  may be formed in one piece with the rigidiser arm  3302 . A boss  3430  may be formed on each side of the frame  3310  and a cavity  3431  may be formed at the end of each extension  3350  to receive the boss. The boss  3430  and cavity  3431  may be shaped and sized to form a secure friction-fit. It should also be understood that the boss  3430  may be formed on the extension  3350  and the cavity  3431  may be provided on the frame  3310  in an alternative example. Additionally, to prevent misassembly the boss  3430  and the cavity  3431  of the right side may be shaped and/or sized differently from the boss and the cavity of the left side. 
       FIGS.  259 A to  259 C  show another example of a rigidiser arm  3302  that may be detachable. A post  3452  and a pair of slots  3453  may be provided to the extension  3350 . The rigidiser arm  3302  may be provided with a hole  3451  to receive the post  3452  and a pair of prongs  3450  may be provided to the rigidiser arm  3302  to engage with respective slots  3453 . To attach the rigidiser arm  3302  to the extension  3350 , the prongs  3450  are first passed through corresponding slots  3453  on the extension and then the post  3452  engages with the hole  3451  to prevent separation of the rigidiser arm from the extension. The bent shape of the prongs  3450  may help secure them when passed through the openings  3453 . Also, the post  3452  may include a head enlarged relative to a shaft of the post to ensure that the post securely engages with the hole  3451 . It should be understood that in other examples that the post  3452  and the slots  3453  need not be provided to the extension  3350  and the hole  3451  and the prongs  3450  need not be provided to the rigidiser arm  3302 , so long as the complementary components are positioned such that the prongs engage the slots and the post engages the hole. Also, more than one post  3452  and more than one hole  3451  may be provided so long as a complementary number is provided. Additionally, more or less than two corresponding prongs  3450  and slots  3453  may also be provided so long as a complementary number is provided. Furthermore, it should be understood that to prevent misassembly the number of prongs  3450  and slots  3453  and the number of posts  3452  and holes  3451  may be different as between the left and right side extensions  3350  and rigidiser arms  3302 . Alternatively, the size and/or shape of the prongs  3450  and slots  3453  and the posts  3452  and holes  3451  may be varied as between the left and right side extensions  3350  and rigidiser arms  3302  to prevent misassembly. 
     Split Back Straps of Positioning and Stabilising Structure 
     According to one aspect, the structure of strap  3301  and positioning and stabilising structure  3300  is of advantage. In particular, the provision of two elastic straps or back strap portions  3317   a ,  3317   b  at the back allows the head to be cupped and the tension vector(s) to be adjusted by suitably positioning them, e.g. by spreading. The provision of two back strap portions  3317   a ,  3317   b  also allows better support and stability, as well as increased flexibility in avoiding specifically sensitive regions of the back of the head. The back strap portions  3317   a ,  3317   b  are intended to cup the head at the calvaria to maintain position and engagement. In one example, depending on the particular head shape of a patient and the amount of splitting of the back strap portions  3317   a ,  3317   b , the upper back strap portion  3317   a  is to be located proximal to the parietal bone and the lower back strap portion  3317   b  is to be located proximal to the occipital bone or superior fibers of the trapezius muscle (i.e. near the nape of the neck or nucha). The lower back strap portion  3317   b  may be configured to engage the head of the patient at a position on or lower than the external occipital protuberance. In contrast to headgear of prior masks which require material length adjustment (shortening or lengthening), the tension provided by the positioning and stabilising structure  3300  is adjustable simply by opening or closing the relative angle between the two back strap portions  3317   a ,  3317   b . To reduce headgear tension, the two back strap portions  3317   a ,  3317   b  are separated further apart on the back of the head when the patient interface  3000  is worn. To increase headgear tension, the two back strap portions  3317   a ,  3317   b  are brought closer together. This manner of adjustment is advantageous over notched straps which only permit preset incremental adjustment of headgear tension, Velcro™ (unbroken loop fabric) straps which require several attempts at fastening and unfastening until the desired headgear tension is obtained, or looping a strap through a buckle that is easier to increase than decrease headgear tension because of the motion of pulling the strap through the buckle for tightening. Also, patients  1000  are afraid to get the headgear tension wrong or to change the headgear tension. 
     The two smaller straps or back strap portions  3317   a ,  3317   b  at the back of the head may be equal in length and not adjustable except through the elasticity of the material or through increasing both in tightness equally by shortening the total length at the side strap portions  3315 ,  3316  of the positioning and stabilising structure  3300 . For example, a sliding mechanism (not shown) may be provided that allows the straps  3301  to be overlapped to a different extent, thus changing the overall length of the positioning and stabilising structure  3300 . Non-independently adjustable strap lengths allow the two back strap portions  3317   a ,  3317   b  to naturally center themselves on the crown of the head. The two back strap portions  3317   a ,  3317   b  may be symmetrical or asymmetrical. In other words, the upper back strap portion  3317   a  may naturally settle at the top of the head, while the lower back strap portion  3317   b  may naturally settle at the back of the head near or below the occipital lobe. This may reduce the possibility of manually over tightening one strap to compensate for the other being too loose resulting in a misfit of the positioning and stabilising structure  3300 . This, again, might not only lead to discomfort but also negatively influence therapy compliance. The aggregated width of both back strap portions  3317   a ,  3317   b  may be substantially equal to the width of a side strap portion  3315 . This is aesthetically pleasing as well as providing a visual indicator to the patient to adjust the back strap portions  3317   a ,  3317   b  when donning the patient interface  3000 . Although two back strap portions  3317   a ,  3317   b  have been described, more are possible which may provide differing degrees of adjustment of headgear tension. When the strap  3301  is in the neutral state and unstretched, the two back strap portions  3317   a ,  3317   b  are partially separated such that a gap exists between them for inviting or indicating to the patient to adjust the back strap portions  3317   a ,  3317   b  when donning the patient interface  3000 . This improves the intuitiveness for adjusting headgear tension, and visually indicates how the headgear tension may be adjusted that is sometimes lacking in prior masks. 
     As indicated above, two or more joints could be provided creating the positioning and stabilising structure  3300  from three, four or more separate straps rather than the strap  3301  being one continuous piece. This might complicate the assembly, but may simplify the manufacturing process. Joints may be placed at the bifurcation point  3324  between the side strap portions  3315 ,  3316  and two back strap portions  3317   a ,  3317   b  or centered at the back. The joints may be sewn, welded, glued, or over molded and could incorporate a high friction material to help reduce movement on the head. High friction materials may include pad printing, silicone printing to increase relative surface friction between the straps  3301 ,  3317   a ,  3317   b  and the patient&#39;s skin or hair in order to maintain position of the straps  3301 ,  3317   a ,  3317   b  on the patient&#39;s head. The high friction materials may be present only on the patient contacting surface of the back strap portions  3317   a ,  3317   b  since the rigidiser arms  3302  may perform some or most of the function of maintaining position of the side strap portions  3315 ,  3316  relative to the patient&#39;s face. 
     High friction materials may also be added to the inside surface of the back and side strap portions  3315 ,  3316 ,  3317   a ,  3317   b , to reduce the straps from slipping against the patient&#39;s face or hair. For the arms or side strap portions  3315 ,  3316  this would help the positioning and stabilising structure  3300  stay on the cheeks and at the back strap portion  3317  it could stop the positioning and stabilising structure  3300  from sliding across the back of the head. Such material may be printed, cast or molded onto the surface or incorporated into joints, sewing or welding processes as mentioned above. Another way to reduce strap slippage is to have elastic yarns protruding from the textile material. 
     Instead of being inserted from the button-holes  3303 ,  3304  located close to the mask frame  3310 , as shown in  FIG.  65   , the rigidiser arm  3302  could optionally be inserted from an opening  3308  located proximal to the bifurcation point  3324  where the positioning and stabilising structure  3300  bifurcates. Once the rigidiser arm  3302  is inserted, the elasticity of the material could be used to hook back the rigidiser arm  3302  inside the opening of one of the small back strap portions  3317   a ,  3317   b  (upper or lower). This may prevent the rigidiser arm  3302  from moving, thus securing it in place. Otherwise the button-holes  3303 ,  3304  could be sewn, molded or otherwise closed permanently in order to trap the rigidiser arm  3302  inside the strap  3301 . 
     The split region  3326  at the back may include two, three or more straps for stability. A positioning and stabilising structure  3300  similar to the described, may be used with full face (covering the nose and mouth) or nasal masks also. Other positioning and stabilising structures of prior masks that may have two or more straps at the back (which may be the same width as the side straps) where the lower back strap typically engages against the head of the patient at a position on or lower than the external occipital protuberance. Such back straps are not stretchable or elastic, but may be length adjustable, and the back straps may be biased to return to a default angle to avoid crinkling and twisting at the convergence point with a single side strap. For example, the default angle may be 45° for the split between two back straps in order to cup and engage the patient&#39;s head, and the pivoting of the back straps relative to each other are for donning and doffing the patient interface to fix the patient interface into a position to provide tension to a seal-forming structure against the patient&#39;s face. The two back straps are biased to return to the 45° angle and therefore only serve the function of cupping the back of the patient&#39;s head for stability of the patient interface and cannot maintain any angle that deviates from the 45° angle. 
     With the use of the present technology, the provision and use of rigidiser arms  3302  may affect the stretchable length of the strap  3301 . This may allow the positioning and stabilising structure  3300  to fit a large range of head sizes. This may effectively be a “one size fits most” positioning and stabilising structure  3300 , which means that the out of the bag positioning and stabilising structure  3300  is more likely to fit a patient even if the patient has not previously tried or used the positioning and stabilising structure  3300 . The present technology may provide a positioning and stabilising structure  3300  that allows easy donning and doffing of the patient interface  3000 . In particular, this may mean that, unlike some other positioning and stabilising structures, the tension settings do not have to change and/or are not lost when the mask  3000  is doffed. The rigidiser arms  3302  may define a desired shape that ensures that there is clearance around the eyes and ears for comfort and visibility. The textile of the strap  3301  may allow the skin to breathe and sweat naturally without silicone, foam or plastics creating and retaining surface heat and condensate from perspiration. 
     The provision of two elastic straps  3317   a ,  3317   b  at the back of the strap  3301  may allow the patient&#39;s head to be cupped and the distribution of the applied force to be adjusted by spreading them and independently changing their position. The two smaller back strap portions  3317   a ,  3317   b  at the back of the head may be equal in length and not adjustable except through the elasticity of the material or through increasing both in tightness equally by shortening the total length at the straps of the positioning and stabilising structure  3300 . 
     Flexible Joint  3305   
       FIGS.  19 ,  71  to  73 ,  75 ,  76  and  166    also show the connection of the positioning and stabilising structure  3300  to the frame  3310  associated with the plenum chamber  3200 . Particularly, the joint  3305  at the rigidiser arm  3302  and the frame  3310  may be flexible and/or elastically deformable. Thus, when donned by the patient  1000 , the seal-forming structure  3100  may be able to accommodate a variety of nasolabial angles (e.g., as shown in  FIG.  2   e   ). It should be understood, therefore, that the flexibility of this joint  3305  may allow the frame  3310 , plenum chamber  3200 , and other associated components to move about a number of axes relative to the rigidiser arms  3302 . In one form of the present technology, the frame  3310  and the plenum chamber  3200  may be rotatable via the flexible joint  3305  about an axis defined between respective ends of the rigidiser arms  3302 . By such an arrangement, the seal-forming structure  3100  may be able to be angled against the inferior region of the patient&#39;s  1000  nose over a wide range of possible nasolabial angles. 
     As can be seen in  FIGS.  18 ,  19 ,  75 ,  76  and  166   , the seal-forming structure  3100  is retained against the underside of the nose of the patient  1000 , one example, against the patient&#39;s airways such as the nares. Proper location of the seal forming structure  3100  is a significant factor in achieving an effective seal of the frusto-cone  3140  against the patient&#39;s nares such that the leaking of pressurized gas is minimized with minimal retention forces. As the frusto-cone  3140  may extend axially from the stalk  3150  of the seal forming structure  3100 , it may be advantageous to allow a degree of flexibility in the orientation of the patient interface  3000  with respect to the patient&#39;s nose to achieve an optimal seal. Such flexibility may be advantageous because patients may have a variety of nasolabial angles (see  FIG.  2   e   ) that may need to be accommodated by a common patient interface. This flexibility may be accomplished in an exemplary patient interface  3000  by providing a flexible joint  3305 . In an example of the present technology, the flexible joint  3305  may be positioned between the frame  3310  and the rigidiser arm  3302 . In such an exemplary arrangement, the frame  3310  may be comprised of a material that facilitates flexing at the flexible joint  3305  with rigidiser arm  3302  of the positioning and stabilising structure  3300 . In an alternative arrangement, it may be the rigidiser arm  3302  that may flex via the extension  3350  to allow proper location of the seal-forming structure  3100  against the underside of the patient&#39;s nose. Additionally, it is also envisioned that flexing may occur partially at both parts. In any of the envisioned arrangements the desired result is that the patient interface  3000  may be able to rotate with respect to the underside of the patient&#39;s nose such that various nasolabial angles may be accommodated. This flexibility provided by the flexible joint  3305  allows the trampoline  3131  to be more effective in providing a comfortable force against the patient&#39;s nares or nose. Without the flexible joint  3305 , the trampoline  3131  would be less effective at accommodating a variety of alar angles and maintaining stability since the stalks  3150  and plenum chamber  3200  would already be in a partially or fully collapsed state when the tension from the positioning and stabilising structure  3300  holds the seal-forming structure  3100  in sealing position against the patient&#39;s airways. 
     This flexible joint  3305  may be provided by forming the frame  3310  and/or the rigidiser arms  3302  from a material having a modulus of elasticity sufficient to allow flexibility in the joint  3305 , while maintaining sufficient stiffness to ensure an effective seal. Additionally or alternatively, the frame  3310  and/or the rigidiser arms  3302  may be shaped structurally to allow for flexibility in this region. In other words, the frame  3310  and/or the rigidiser arms  3302  may be shaped to allow the requisite amount of flexibility in the region of the joint  3305 . This may be accomplished by removing portions of these structures such that their stiffness is reduced to allow flexing. 
     A further possible advantage of this aspect of the technology may be that it reduces the bending moment associated with the rigidiser arms  3302  and the frame  3310 . As shown in  FIGS.  19 ,  71  to  73  and  75   , the rigidiser arms  3302  may be shaped to conform to the contours of the patient&#39;s face. Also, when the seal-forming structure  3100  engages with the patient&#39;s nares, they may cause displacement of the frame  3310  due to the relatively limited amount of flexibility between the seal-forming structure  3100 , the plenum chamber  3200 , and the frame  3310 , which are held against the nose by the positioning and stabilising structure  3300 . By providing a flexible joint  3305  between the frame  3310  and the rigidiser arms  3302 , the bending moment associated with these structures when the patient interface  3000  is donned by the patient may be reduced because some of the associated forces may be dissipated into the flexing of the joint. This may be advantageous because the patient interface  3000  would then be subjected to less force during use to reduce wear and tear. Also, by dissipating these forces into the bending of the flexible joint  3305 , bending of the rigidiser arms  3302  and/or the frame  3310  may be reduced. This may be advantageous because if the rigidiser arms  3302  are shaped to conform to the face of the patient, then bending them may reduce the conformity, resulting in discomfort to the patient. The same may be true for bending of the frame  3310  and bending of the frame  3310  may also cause the seal-forming structure  3100  to be displaced from the patient&#39;s nose. 
     It should also be understood that in the arrangement discussed above, it may be advantageous to stiffen the rigidiser arms  3302 . By forming the rigidiser arms  3302  from a material that is sufficiently stiff and/or shaping the rigidiser arms  3302  such that they are sufficiently stiff, it may be possible to ensure that the flexible joint  3305  does not allow the seal-forming structure  3100  to displace from the patient&#39;s nose. In other words, a proper fit and effective seal may be accomplished by sufficiently stiff rigidiser arms  3302  that maintain the desired degree of conformity to the patient&#39;s face while allowing sufficient displacement of the seal-forming structure  3100  such that it can engage the patient&#39;s nose and provide an effective seal. The rigidiser arms  3302  may be formed from Hytrel® with a flexural modulus of 180 MPa at 23° C. and a tensile modulus of 180 MPa ( 26 ). It should also be understood that in one aspect of the technology, the patient interface  3000  may be structured such that elastic deformation takes place only at the seal-forming structure  3100  and at the flexible joint  3305  between the frame  3310  and the rigidiser arms  3302 . 
     In the example of the present technology described without a flexible joint  3305 , the extension  3350  of the rigidiser arm  3302  performs a similar function to the flexible joint  3305  as described above. 
     Tension Vectors of Positioning and Stabilising Structure 
     As mentioned above, the exemplary positioning and stabilising structure  3300  may advantageously locate the headgear tension vectors with respect to the patient&#39;s head such that the compression vectors associated with the seal-forming structure  3100  are properly aligned with the nose or nares of the patient. As shown in  FIGS.  72 ,  73 ,  75  and  76   , a vector V is depicted to indicate an exemplary direction and magnitude of a force that urges the seal-forming structure  3100  against the nose of the patient  1000  in use. By attaching the exemplary positioning and stabilising structure  3300  operatively to the seal-forming structure  3100 , the tension of the positioning and stabilising structure  3300  when worn by the patient  1000  may be sufficient to urge the patient interface  3000  against the nose or nares of the patient  1000  with a force having the direction and magnitude of the vector V. The concept of the vectors may be explained as follows. To properly and/or effectively form a seal about the nares of the patient  1000 , when using nasal pillows  3130  as depicted in this example of the technology, the seal-forming structure  3100  should be urged against the patient&#39;s nares in a direction substantially coaxial to the longitudinal axes of respective stalks  3150  of the seal-forming structure  3100 . The magnitude of the force must also be sufficient to allow the seal-forming structure  3100  to seal around the nares, but not so great as to cause discomfort or deformation of the relatively soft seal-forming structure  3100 . Therefore, a force of the magnitude and direction depicted as the vector V must be provided to the seal-forming structure  3100 . However, it is not ideal to have straps  3301  draped across the eyes and along the sides of the patient&#39;s nose or across the ears. This may be uncomfortable and disruptive to the patient  1000 . Two point force and vector control allows the strap  3301  to gently stabilise the mask  3000  and pull the nasal pillows  3130  into place and form a pneumatic seal with the patient&#39;s airways. 
     To overcome this problem of needing to provide sealing forces of a requisite direction and magnitude while displacing them from certain regions of the patient&#39;s face, the rigidiser arms  3302  and/or frame  3310  described above may be provided. The rigidiser arms  3302  and/or frame  3310  may act as an intermediary for transferring tension forces from the positioning and stabilising structure  3300  to the seal-forming structure  3100 , while allowing the straps  3301  to be directed away from the patient&#39;s eyes. In other words, the positioning and stabilising structure  3300 , by virtue of being in tension, may generate a force at one end of a respective rigidiser arm  3302  and/or frame  3310 , which being sufficiently stiff, transmits this force having an equivalent direction and magnitude to its opposite end where the seal-forming structure  3100  is located. Thus, the seal-forming structure  3100  may be urged against the patient&#39;s nose to form an effective seal. Said another way, the rigidiser arms  3302  and/or the frame  3310  serve to structurally decouple the positioning and stabilising structure  3300  from the seal-forming structure  3100  while continuing to maintain sealing forces of an adequate direction and magnitude. 
     As described above, the straps  3301  of the positioning and stabilising structure  3300  may surround the rigidiser arms  3302  in certain examples. To facilitate the force decoupling described in the preceding paragraphs while maintaining this sheath-like arrangement of the straps  3301  and rigidiser arms  3302 , the rigidiser arms  3302  may comprise a smooth surface along at least a portion thereof. By providing a smooth surface along the rigidiser arms  3302 , the straps  3301  of the positioning and stabilising structure  3300  may extend and/or compress along the rigidiser arms  3302  in a relatively free and/or low friction fashion. In other words, the straps  3301  float over the rigidiser arms  3302  except at the pocketed ends  3311  where it is secured to the rigidiser arms  3302 . Moreover, by reducing friction of the positioning and stabilising structure  3300  along the rigidiser arms  3302 , extraneous and undesired forces may be avoided, which may in turn result in a loss or disruption of the pneumatic seal of the seal-forming structure  3100  and/or an uncomfortable fit. 
     Some positioning and stabilising structures of prior masks that have a multi-layered laminated strap where there are layers made from different materials providing different degrees of flexibility permanently laminated to each other. Other positioning and stabilising structures of prior masks use stitching or adhesives to permanently connect the multi-layered strap together. In contrast, the positioning and stabilising structure  3300  of the present technology has a strap  3301  that is releasably engageable with the rigidiser arm  3302 . This permits separate washing of the strap  3301  from the rigidiser arm  3302  and frame  3310 . The releasable engagement is provided in a small area localised region (the edge of the rigidiser arm  3302  proximal to the frame  3310 ) using a pocketed end  3311  of the strap  3301  which permits stretch of substantially the entire length of the strap  3301  from the point of connection with the frame  3310 . Other positioning and stabilising structures of prior masks may use an adjustment buckle or Velcro™ to adjust the length of one or more headgear straps (usually by shortening the length) in order to adjust the headgear tension of the patient interface  3000  on the patient&#39;s face. In contrast, the positioning and stabilising structure  3300  of the present technology does not require length adjustment to adjust the headgear tension and is particularly beneficial for patients with arthritic hands who may lack fine motor skill to be able to properly an adjustment buckle or Velcro™ for headgear tension adjustment, especially in a darkened room. 
     Manufacturing the Strap 
     A positioning and stabilising structure  3300  is manufactured to shape (e.g., formed in one piece to shape otherwise known as “fully-fashioning” without the need to cut away any substantial amounts of material) thereby producing little or no waste material. Alternatively, the positioning and stabilising structure  3300  may be divided into segments that are each manufactured to shape separately (e.g., by knitting) and then attached to one another.  FIG.  132    demonstrates a single, unitary seamless structure having at least two regions (e.g. the crown portion or rear portion  210  and straps  220 ), wherein the at least two regions extend from a junction (the junction being the connection between the straps  220  and the rear portion  210 ), where the straps  220  extend at a different angular orientation to the rear portion  210 . The rear portion  210  and straps  220  are formed in a continuous process (i.e. the material that makes up the component and the shape of the component are formed in a single step)—this is different to a process where a sheet of material is made and then cut to shape (this would not be considered a single step).  FIG.  132    also shows that the straps  220  branch out or extend at a different angle or direction to the rear portion  210 , without requiring seams or additional formation steps. 
     A knitted component such as a positioning and stabilising structure  3300  is defined as being formed of “unitary knit construction” when constructed as a one-piece knit element that is substantially free of additional stitching or bonding processes. 
     As shown in  FIG.  133   , the straps  220  may be formed (e.g., by warp knitting, circular knitting or 3D braiding) as a continuous piece that is subsequently cut as this procedure may further increase manufacturing efficiency. 
     Knitting various positioning and stabilising structure sections in a continuous manner may be advantageous as there are no or very few additional manufacturing steps that would be required to sew, fuse, adhere or otherwise attach adjoining sections. As a result, the manufacturing process may have reduced steps, the amount of material waste is reduced, there would be virtually no seams in the positioning and stabilising structure  3300  between the adjoining sections, and the positioning and stabilising structure  3300  made of a fabric without distinctive joins or seams may be more comfortable for patients. 
     Techniques 
     A number of techniques can be used in accordance with the present technology to manufacture a positioning and stabilising structure  3300  to shape with little or no waste material. The technique may produce a positioning and stabilising structure that is a single, unitary, seamless structure. Techniques that may produce a single unitary seamless structure include mechanical manipulation of yarn including interlooping (such as knitting), interweaving and/or intertwining (including braiding, knotting and crocheting). An alternative technique of 3D printing may also create a positioning and stabilising structure having a unitary, seamless structure. 
     A manufacturing technique in accordance with the present technology may have one or more of the following features: (1) produces little or no waste; (2) produces a positioning and stabilising structure that is comfortable for the patient; (3) produces a positioning and stabilising structure that is conformable; (4) produces a positioning and stabilising structure that is breathable; (5) produces a positioning and stabilising structure that may minimize facial marking; and/or 6) produces a positioning and stabilising structure that is lightweight. 
     Interlooping—Knitting 
     In accordance with an example of the present technology, a positioning and stabilising structure  3300  may be formed by interlooping such as knitting (e.g., threading yarn or thread to form a knitted fabric). The positioning and stabilising structure  3300  may be formed by flat knitting or circular knitting, however other forms of knitting may also be possible. Flat knitting and circular knitting may be advantageous as they are able to create a positioning and stabilising structure  3300  with a unitary, seamless structure. Flat or circular knitting machines may be utilized to create a weft knit or a warp knit. A variety of knitting processes including circular knitting and warp- or weft-flat knitting, may be utilized to manufacture the positioning and stabilising structure component or components. Flat knitting may have some advantages, including but not limited to (1) the ability to locate floating yarns within, for example, a positioning and stabilising structure strap, in order to provide extra cushioning or bulk, and/or (2) the ability to include extra loops of yarns on either the upper or lower surface of the positioning and stabilising structure strap, thus creating the effect of a soft terry cloth material, for example, or creating an unbroken loop fabric for engagement with a hook tape fastener, and/or (3) the ability to knit a 3D dimensional spacer fabric construction adjacent to double-faced knit construction within a single unified positioning and stabilising structure construction. 
     The positioning and stabilising structure  3300  may be formed primarily from multiple yarns that are mechanically manipulated through an interlooping process to produce a single unitary structure having various sections with different physical properties. 
       FIG.  134    illustrates the wale of a weft knit fabric  64 , or the direction that the loops of one thread join to a loop of another thread. The course  85 , or the direction of the loops from a single thread is shown in  FIG.  135   .  FIGS.  136  and  137    illustrate a basic closed loop warp knit  90 .  FIG.  138    illustrates an example of a warp knit tricot jersey fabric structure in which a yarn is knitted in a vertical direction in a zig-zag manner, capturing other warp yarns, with the wale running somewhat parallel to the course. 
     Referring to  FIGS.  136  to  139   , a warp knit  90 ,  90 - 1  comprises the wales and courses running parallel to one another, while in a weft knit  100  the wales run perpendicular to the course. The positioning and stabilising structure  3300  of the present technology may be formed by either warp knit or weft knit. A warp knit, for example tricot, raschel or locknit, is typically more resistant to runs, easy to machine, and may utilize multiple yarns (allowing for the use of multiple colors or yarn types). A weft knit  100  can be formed with a single yarn; however, use of multiple yarns is also possible. The positioning and stabilising structure  3300  of the present technology may be constructed of a warp knit or a weft knit. 
     Knitted fabrics may have different stretchability characteristics compared to woven fabrics. Knitted fabrics are typically more flexible than woven fabrics, which may only stretch in one direction (depending on the yarn they are made from), and therefore may provide a more comfortable fit for the patient. Knitted textiles may be constructed in such a way that the fabric has a two-way stretch—i.e. a first yarn oriented in a first direction has a lower flexibility than a yarn oriented in a second direction. This arrangement may be desirable along the straps of the positioning and stabilising structure  3300  such that the straps can stretch along their length but not across their width, or vice versa. Alternatively, the knitted textile may have a four-way stretch i.e. yarn in a first direction and a second direction and both are flexible such that application to a strap would allow stretch in both lengthwise and crosswise directions. 
     The example of  FIG.  142    shows a strap  1200  having a grain or course  1250 , and illustrates how the direction of the grain or course affects stretch. The knitted fabric will tend to stretch more readily in the direction of the course. Therefore, the positioning and stabilising structure  3300  may be designed to stretch in certain directions and be more resistant to stretch in other directions. For example, the strap  1200  will tend to stretch in its width direction A (from the patient&#39;s face to the back of the head) and may have limited stretch along the length of the strap. This configuration may increase stability of the positioning and stabilising structure  3300  in the lengthwise direction while increasing fit range. The strap  1200  may be configured to stretch in certain directions and be resistant to stretch in other directions in order to better enable the strap  1200  to hold a mask assembly on a patient&#39;s face in a manner that enhances the seal with the patient&#39;s face. 
     Referring to  FIGS.  140  and  141   , a knitted strap  1105  includes a top portion  1102 , a rear portion  1104 , and a lower portion  1106 . The lower portion  1106  may bifurcate or branch out at a junction to form the top portion  1102  and the rear portion  1104 . The angular orientation of the top portion  1102  may be different compared to the rear portion  1104  e.g. the top portion  1102  may extend at about 30-110 degrees, or about 90 degrees or perpendicular to the rear portion  1104 . The direction of the knit, or the grain or course  1150  of the knit, may be altered to adjust the shape or stretch of the fabric in certain areas. For example, the grain or course  1150  may be configured to curve the strap at a cheek region to avoid obstructing the patient&#39;s eyes. Further, as shown in  FIG.  141   , the grain or course  1150  may curve, as shown by the arrows B, to a split thereby forming the top portion  1102  and the rear portion  1104 . Such configurations of the top portion  1102  and the rear portion  1104  may stabilize the straps in position on the patient&#39;s head and thus better enable the knitted strap  1105  to hold a mask assembly on a patient&#39;s face in a manner that enhances the seal with the patient&#39;s face. 
     The knitted strap  1105  may support a patient interface  3000  (e.g., a nasal mask) on the patient&#39;s face. A connector  1120  may be used to attach the strap  1105  to the patient interface  3000 , and an air circuit  4170  may deliver breathable gas to the patient&#39;s airways via the patient interface  3000 . In the illustrated example, the patient interface  3000  is positioned under the patient&#39;s nose and seals against the external surfaces of the patient&#39;s nose. 
     The positioning and stabilising structure  3300  of the present technology may further comprise a pocket, tunnel, layers and/or ribs. Such positioning and stabilising structures  3300  may be formed in one piece by circular or flat knitting. The pockets or tunnels may be reinforced with materials having a higher stiffness or rigidity than the knitted textile, thereby rigidising the positioning and stabilising structure  3300 . Rigidising the positioning and stabilising structure  3300  may better stabilize the mask in position on the user&#39;s face. Materials used for rigidising the positioning and stabilising structure  3300  may include plastics such as nylon, polypropylene, polycarbonate, or higher stiffness textiles such as braided ropes. The rigidising of the positioning and stabilising structure  3300  may be positioned at bony regions of the patient&#39;s head, for example the cheeks, occiput or crown. The reinforcing structure may be inserted during the knitting process, for example, a stiffer or flatter yarn or a rigid polymer element may be inserted into the knit construction, during or after the knitting process. The strands or rigid components would function to withstand tension and bear the stresses e.g., due to tightening of the positioning and stabilising structure straps for therapy, or to stabilise the mask better, or would assist to act as coupling or fastening agents to attach the positioning and stabilising structure piece(s) to the mask interface. 
     Alternatively, the pockets or tunnels may be cushioned to add comfort. For example, pockets or tunnels may be filled with foam, gel, floating yarn, looped yarn or other cushioning material. 
     The positioning and stabilising structure  3300  may be formed by flat knitting or circular knitting, wherein the positioning and stabilising structure  3300  has selvedges. That is, the positioning and stabilising structure  3300  may be formed to have a finished configuration such that the ends of the yarns used to construct the positioning and stabilising structure  3300  are substantially absent from the edges of the positioning and stabilising structure components. An advantage of fashioning the positioning and stabilising structure components to the finished shape is that the yarns are not being cut, and are thus less likely to unravel and may require fewer finishing steps. By forming finished edges, the integrity of the positioning and stabilising structure  3300  is maintained or even strengthened and fewer or no post-processing steps are required to either (1) prevent unravelling of the positioning and stabilising structure component and/or (2) create an edge that is distinct yet soft (such as in ultrasonically cutting and sealing a ‘soft edge’ on a fabric-foam-fabric laminate material) and/or (3) enhance the aesthetic and durability characteristics of the positioning and stabilising structure  3300 . 
     The positioning and stabilising structure  3300  of the present technology may be formed by a regular or irregular pique knit. A pique knit will orient a first yarn on the right side (non-patient contacting side that is visible once the positioning and stabilising structure  3300  is donned) and a second yarn on the wrong side (the patient contacting side that is not visible once the positioning and stabilising structure  3300  is donned). That is, the yarn exposed on the right side may be different to the yarn exposed on the wrong side. For example, the yarn on the right side may have a pleasant visual appearance and the yarn on the wrong side may have a nice hand feel for contacting the patient&#39;s skin. Alternatively, or in addition, the yarn on the right side may have a first moisture wicking property and the wrong side may have a second moisture wicking property. For example, the yarn on the right side may have a high percentage of microfiber having a first moisture wicking property and the wrong side may have a high percentage of non-microfiber having a second moisture wicking property. 
     The positioning and stabilising structure  3300  may be formed as a unitary knit structure which may also be uniform in material and properties, for simplicity, but it may be formed as a unitary structure including various sections that have different physical properties, joined in a seamless manner. The various sections may exhibit, for example but not limited to, different degrees of strength, abrasion resistance, wear resistance, flexibility, enhanced durability, higher or lower moisture absorption (moisture absorbability), moisture-wicking ability, water affinity, breathability or air-permeability, liquid permeability, stretch or stretch-resistance, compressibility, cushioning ability, support, stiffness, recovery, fit, and form. The various sections may be constructed to exhibit variations in directional stretch, such as four-way stretch, or bi-directional stretch, a tailored level of stretch resistance, or no stretch. This may be achieved by, for example but not limited to, selecting a particular yarn or knit construction type. 
     The positioning and stabilising structure  3300  as a unified seamless structure may be formed in one piece with uniform characteristics, or from two or more sections with varying characteristics. The two or more positioning and stabilising structure sections may differ by way of using two or more different yarns of different twist, denier, fibre composition, etc., thus imparting different physical properties to the positioning and stabilising structure  3300 . The two or more positioning and stabilising structure sections may differ by way of using two or more various knit stitch types, thus imparting unique physical properties to the two sections. 
     Whereas one region may incorporate, for example, elastane or PBT (Polybutylene terephthalate polyester) to enhance stretch, the other region may incorporate, for example, nylon or polyester to enhance durability. Similarly, while one region of the positioning and stabilising structure  3300  may incorporate yarn with one denier, the other region may include a yarn with a greater or reduced denier, crimp or texture, in order to customize the cushioning, thickness or bulk. 
     The two or more sections within a positioning and stabilising structure construction may be connected by using tuck stitches or other knit stitches that, for example, join a first section to a second section in a seamless manner. This would be achieved by knitting the first section, then knitting the tuck stitches between the first knitted section and a second knitted section, then knitting the second section. The tuck stitches are utilized to seamlessly connect sections between wales, especially when using a narrow-tube circular knitting machine. 
     The positioning and stabilising structure piece may be finished without a seam. If it is made with an un-dyed yarn, this may be achieved by finishing the knitting process with a yarn that contains water-soluble fibres. The water-soluble fibers permit the fabric to shrink in the dyeing process and provide a neatly-finished edge, eliminating the need to create an additional seam on the edge. 
     In order to enhance manufacturing efficiency, knitting machines may also be utilized to form a series of joined positioning and stabilising structure components, such as straps or crown components. That is, the knitting machines may form a single component that includes a plurality of positioning and stabilising structure pieces. Each of the positioning and stabilising structure segments may have substantially identical shapes and sizes. Alternatively, each of the positioning and stabilising structure pieces may even have different shapes and sizes, which may be programmed in sequence. Moreover, a knit release area (which may consist of, for example but not limited to, dissolvable yarns, loosely knitted yarns, finer denier yarns or easy-to-tear placeholder yarns) may be knitted into the series of positioning and stabilising structure components in order to allow the various positioning and stabilising structure parts, for example, straps, to be separated without the need for cutting operations. 
     Variable Thread Count 
     In another example, the thread count may vary across the fabric to enhance comfort, fit and/or performance. For example, the thread count may be higher in regions requiring greater stiffness (e.g., cheek region, occiput). In regions (e.g., along the straps) where a lower stiffness is desired, however, the thread count may be lower thereby permitting the material to flex more easily. 
     The thread count, and therefore the stiffness, may be determined by the type of yarn, the type of stitch (e.g., a criss-cross stitch may be stiff), and the distance between stitches. 
     Yarn 
     Yarn may be utilized to create the positioning and stabilising structure  3300  of the present technology. The yarn may be synthetic, and may be twisted or textured, and could be made from, but not limited to nylon, polyester, acrylic, rayon, or polypropylene. The yarn could be a conventional staple yarn, a microfiber yarn, or combination of both. The yarn may incorporate an elastane fiber or filament to provide stretch and recovery properties, such as fibers bearing the LYCRA trademark from the DuPont Company. The yarn may be made of synthetic materials, or natural fibres such as cotton, wool or bamboo, or natural filament such as silk. 
     The yarns used to construct any component of the positioning and stabilising structure may be formed of a monofilament or a plurality of single filaments, that is, a multifilament yarn. 
     The yarn may include separate filaments that are each formed of different materials. The yarn may also include filaments that are each formed of two or more different materials, such as bicomponent yarn with filaments having a sheath-core configuration or two halves formed of different materials. Different degrees of twist or crimping, as well as different deniers, may affect the properties of the positioning and stabilising structure  3300 . 
     The materials utilized to construct the positioning and stabilising structure components  2900  may be made recyclable or biodegradable, for example, the yarns may include recyclable or biodegradable fibers or filaments. 
     Areas of the positioning and stabilising structure  3300  subject to greater wear (for example but not limited to areas or regions coming into contact with a patient&#39;s pillow), such as an area of positioning and stabilising structure  3300  located at the back of the head or nape of the neck, may possibly be more densely fabricated and may thus be a heavier weight and less extensible. Conversely, this area may be subject to the greatest amount of moisture accumulation through sweat, and therefore may need to be made of a thin, yet strong, net-like construction with a custom aperture pattern. In this case, the abrasion-resistance may need to be inherent in the yarn properties only. 
     3D Printing 
     In another example, positioning and stabilising structure  3300  may be manufactured to shape using a 3D printer. As shown in  FIG.  143   , a 3D printer may be used to print a plurality of connected links  2802  thereby forming a flexible 3D printed textile  2804 . Referring to  FIG.  144   , a positioning and stabilising structure piece  2900  may be formed to include a rigidiser arm  3302 . The rigidiser arm  3302  includes holes  2922  through which the links of the textile  2804  may pass as the textile  2804  is printed to integrate the textile  2804  and the rigidiser arm  3302 . The rigidiser arm  3302  could be made from any suitable material (e.g., a polymer such as Nylon 12 or a sintered solid from a metal powder, or any other material able to be used as an additive manufacture process). As the additive manufacture (“3D Printing” process technologies improve, it is envisioned that the material selection will become broader for the purposes of 3D printing textiles, with the optional inclusion of a rigid component such as the rigidiser arm  3302 . Structure could be inherent in material or by virtue of shape, form or structure. 
     Further, as shown in  FIG.  145   , a 3D printed strap  2924  may be integrated into holes  2912 ( 1 ),  2914 ( 1 ) of male and female clips  2912 ,  2914 . 
     Fashioning and Finishing the Strap 
       FIGS.  79  and  80    show views of the strap  3301  at an intermediate step of production. The exemplary strap  3301  shown is a raw length of strap that has not been cut to length from the knitted material produced, in examples, by the methods and processes described above. For example, a pair of button-holes  3303  can be seen at the left-most end of the strap  3301 , however, once finished only hole will be at that end because the raw strap will have been cut between those holes to produce the strap shown in  FIG.  81   . Also, the knitting process that forms the raw length of strap  3301  shown in  FIG.  79    forms multiple split regions  3326  along the length of the strap. However, the finished strap  3301  shown in  FIG.  81    only includes one split region  3326 . Again, this is because during finishing the strap  3301  will be cut between the right-most button-hole  3303  shown in  FIG.  79    to separate the raw length of strap  3301  shown there into multiple straps. 
     According to one example of the technology, the strap  3301  may be formed using a warp labelling machine with multiple bars to form chains in the fabric. According to another example, the strap  3301  may be formed by a Comez machine with six bars for joining the two side strap portions  3315 ,  3316  and the two back strap portions  3317   a ,  3317   b  in the center. By adding more bars to the Comez machine more directions of knitting may be accommodated. The knitting process may also include forming the strap  3301  with a different weave at the bifurcation point  3324 . The material of the strap  3301  may include a 1740 count. The order of pattern types for knitting a strap  3301  may be as follows: normal, then button-hole, then normal, then split, then normal, then button-hole, and then normal. A subsequent strap  3301  would then be knitted with this same order again going forward for each strap  3301  produced. 
     In one example of the present technology, the thread used for knitting the strap  3301  may be double helically wound. 
     To add further strength at potential failure points, the strap  3301  may be formed with extra stitching at these points. Potential failure points may include the button-holes  3303 ,  3304  and the bifurcation points  3324 . Also, additional threads may be knitted along the middle of the strap  3301  for additional reinforcement. 
       FIG.  80    shows a cross-sectional view of the side strap portion  3316  of  FIG.  79    taken through line  80 - 80 . A bifurcation point  3324  can be seen to indicate the split region  3326  of the side strap portion  3316  and the division between the upper back strap portion  3317   a  and the lower back strap portion  3317   b.    
       FIG.  79    also indicates dimensions L 1 -L 6  for the various features of the strap  3301 . L 1  indicates a distance between a button-hole  3303  of one strap  3301  and a button-hole  3303  of an adjacent strap. In one example of the technology L 1  may be about 515 mm. L 2  indicates a distance between button-holes  3303  of the same strap  3301  and this value may, according to one example, be about 500 mm. L 3  indicates the length of the split region  3326  which may be about 200 mm in one example of the technology. L 4  may indicate the distance between adjacent button-holes  3303  of adjacent straps  3301  and may be about 15 mm in one example. L 5  may indicate the width of a button-hole  3303  and may be about 5 mm in one example. L 6  may indicate the width of the strap  3301  and may be about 15 mm in one example. 
       FIGS.  81  to  83    show views of a finished strap  3301  according to an example of the present technology. As can be seen in  FIG.  81    there is only one split region  3326  and only one button-hole  3303  at each end of the strap  3301 . Therefore, it should be understood that this strap  3301  has been cut and finished from the strap  3301  shown in  FIG.  79   , according to an example of the technology. Also, shown in  FIG.  81    is a strap logo  3357  that may be formed on the strap  3301  in the form of a corporate logo or other artwork, for example. The strap logo  3357  may be formed by pad printing or ultrasonic welding. If the strap logo  3357  is formed by ultrasonic welding this may help to splay the back strap portions  3317   a ,  3317   b  at the bifurcation points  3324  to encourage spreading the back strap portions  3317   a ,  3317   b  by the patient  1000  to ensure ideal fitment and strap tension. 
       FIG.  81    also shows end welds  3311 . 1 ,  3313 . 1 . As described above, the side strap portion  3316  may be knitted into a hollow or tube-like shape. Thus, the ends will be open if not closed by welding, for example, which prevents tearing along open ends. The end welds  3311 . 1 ,  3313 . 1  may be formed by ultrasonic welding to seal loose fibers of the strap  3301 . While ultrasonic welding may reduce the stretchability of the fabric that comprises the strap  3301  it may serve to reduce fraying at the ends and to add strength at high stress points. Since the end welds  3311 . 1 ,  3313 . 1  are proximal to the respective pocketed ends  3311 ,  3313  the end welds provide strength for the strap  3301  to be retained to the rigidiser arms  3302  at their respective protruding ends  3306 . It should be understood that the pocketed ends  3311 ,  3313  and their respective end welds  3311 . 1 ,  3313 . 1 , according to one example of the technology, are the primary portion of the strap  3301  for retention and/or anchoring to the rigidiser arms  3302 . The strap  3301  may lose elasticity after prolonged use but it should be understood that by washing and drying the strap  3301  at least some or all of this elasticity may be recovered. 
     The StretchWise™ headgear provided by Fisher &amp; Paykel™ for the Pilairo™ mask has a rigid detachable pivotal connection between rigid plastic hooked ends of the headgear strap and rigid plastic vertical bars located on the mask frame. In contrast, the strap  3301  of one example of the present technology does not have a rigid detachable connection between the strap  3301  and the mask frame  3310  which avoids problems such as creep and breakage of hooked ends after repeated engagement and disengagement of rigid components. A significant amount of force is required to materially deform the rigid hooked ends of the StretchWise™ headgear to engage and disengage it from the rigid bars. In contrast, the rigidiser arms  3302  of the present technology are inserted into button-holes  3303  of the strap  3301  and retained in a pocketed end of the strap  3301  without such a significant force because no plastic deformation of either the rigidiser arm  3302  or the strap  3301  is required to connect or disconnect the strap  3301  to and from the mask frame  3310 . Another deficiency of the StretchWise™ headgear is that elasticity of the headgear strap does not recover to substantially the original level of elasticity after washing the headgear strap. In other words, the StretchWise™ headgear will become looser over time. 
       FIG.  82   , similar to  FIG.  80   , shows a cross-sectional view of the strap  3301  taken through line  83 - 83  of  FIG.  81   . The bifurcation point  3324  can be seen that indicates the initiation of the split region  3326 . Also, the strap logo  3357  can be seen raised from the side strap portion  3316  in this view. 
       FIG.  83    shows a detailed view of the strap  3301  and particularly shows the strap logo  3357 . Also, the bifurcation point  3324  can be seen at the beginning of the split region  3326 . 
       FIG.  81    also shows additional dimensions that describe features of the exemplary strap  3301 . L 7  may indicate the distance between the finished end of the strap  3301  at the end weld  3311 . 1 ,  3313 . 1  and may be about 5 mm in one example. L 8  may indicate the width of the end welds  3311 . 1 ,  3313 . 1  and may be about 1 mm in one example. 
     Donning the Patient Interface and Positioning and Stabilising Structure 
     An exemplary patient interface  3000  and positioning and stabilising structure  3300  may be donned in a simple yet adjustable manner according to various examples of the present technology. As will be described in greater detail below,  FIGS.  84  to  112    depict various sequences of a wearer (i.e., a patient)  1000  donning and adjusting the patient interface  3000  and positioning and stabilising structure  3300 . 
       FIGS.  84  to  88    show a series of perspective views of a patient  1000  donning the patient interface  3000  and positioning and stabilising structure  3300 . In  FIG.  84    the patient  1000  begins donning the patient interface  3000  and positioning and stabilising structure  3300  by holding the patient interface  3000  and placing the seal-forming structure  3100  against the nose.  FIG.  85    then shows the patient  1000  beginning to don the positioning and stabilising structure  3300 . The patient  1000  pulls the strap  3301  near the split region  3326  with one hand while holding the patient interface  3000  with the other hand to stretch the strap  3301  over the head.  FIG.  86    then shows the patient  1000  pulling the strap  3301 , while still holding the split region  3326  with one hand and the patient interface  3000  with the other, further towards the back of the head. At the completion of this step the strap  3301  should be located at the back of the head near the crown and near or above the occipital lobe so that proper tension sealing force is placed on the positioning and stabilising structure  3300  to hold the patient interface  3000  against the patient&#39;s  1000  nose.  FIG.  87    then shows the patient  1000  adjusting the positioning and stabilising structure  3300  to locate the rigidiser arms (not visible in these views) under the cheek bones and to adjust the fit of the seal-forming structure  3100  against the nose to ensure a complete seal. By locating the rigidiser arms  3302  under the cheek bones the positioning and stabilising structure  3300  may be prevented from riding up on the face of the patient  1000  and into the patient&#39;s line of sight.  FIG.  88    then shows the patient  1000  with the patient interface  3000  and positioning and stabilising structure  3300  donned and prepared for therapy. 
       FIGS.  89  to  93    show a series of side views of a patient  1000  donning the patient interface  3000  and positioning and stabilising structure  3300 .  FIG.  89    shows the patient  1000  holding the patient interface  3000  in one hand and raising it toward the nose while holding the strap  3301  of the positioning and stabilising structure  3300  in the other hand. At this point the strap  3301  may not be significantly stretched.  FIG.  90    shows the patient  1000  locating the patient interface  3000  against the nose, particularly the seal-forming structure  3100 , with one hand and pulling the strap  3301  of the positioning and stabilising structure  3300  to stretch it over the head with the other hand. A separation at the split region  3326  can be seen as well due to the pulling of the strap  3301 .  FIG.  91    shows the patient  1000  still holding the seal-forming structure  3100  and the patient interface  3000  against the nares while pulling the strap  3301  of the positioning and stabilising structure  3300  further toward the back of the head. At this point, the initial step of donning the patient interface  3000  and positioning and stabilising structure  3300  should be nearly complete such that the strap  3301  is located against the back of the patient&#39;s  1000  head.  FIG.  92    then shows the patient  1000  adjusting the seal-forming structure  3100  and the patient interface  3000  against the nose to ensure a proper seal and proper location of the rigidiser arms  3302  relative to the cheek bones.  FIG.  93    then shows the patient  1000  with the patient interface  3000  and positioning and stabilising structure  3300  donned and prepared for therapy. 
       FIGS.  94  to  98    show a series of front views of a patient  1000  donning the patient interface  3000  and positioning and stabilising structure  3300 .  FIG.  94    shows the patient  1000  beginning to don the patient interface  3000  and positioning and stabilising structure  3300 . Holding the patient interface  3000  with one hand and the strap  3301  of the positioning and stabilising structure  3300  with the other hand, the patient  1000  raises the patient interface and positioning and stabilising structure toward the face.  FIG.  95    shows the patient  1000  with the positioning and stabilising structure  3300  in one hand and the strap  3301  slightly stretched.  FIG.  95    also shows the patient interface  3000  held in the other hand and near the nose for placing the seal-forming structure  3100  against the nose.  FIG.  96    shows the patient  1000  having stretched and pulled the strap  3301  of the positioning and stabilising structure  3300  over the head and locating the strap  3301  against the back of the head while holding the seal-forming structure  3100  and the patient interface  3000  against the nose.  FIG.  97    shows the patient  1000  then adjusting the positioning and stabilising structure  3300  and the patient interface  3000  by locating the rigidiser arms  3302  in a comfortable position to seat under the cheek bones so that the positioning and stabilising structure  3300  does not ride up into the patient&#39;s line of sight and a seal can be maintained against the nares with the seal-forming structure  3100 .  FIG.  98    then shows the patient  1000  with the patient interface  3000  and positioning and stabilising structure  3300  donned and prepared for therapy. 
       FIGS.  99  to  104    show a series of perspective views of a patient  1000  donning the patient interface  3000  and positioning and stabilising structure  3300 .  FIG.  99    shows the patient  1000  beginning to don the patient interface  3000  and positioning and stabilising structure  3300  by stretching the strap  3301  while holding the strap  3301  with one hand and the patient interface  3000  with the other hand.  FIG.  100    then shows the patient  1000  placing the patient interface  3000  and positioning and stabilising structure  3300  on the head by raising the patient interface  3000  toward the face and pulling the strap  3301  over the back of the head.  FIG.  101    then shows the patient  1000  placing the seal-forming structure  3100  against the nares with one hand while holding the strap  3301  in a stretched state near the back of the head.  FIG.  102    then shows the patient  1000  locating the strap  3301  at the back of the head by beginning to release its tension sealing force. The patient  1000 , in  FIG.  102   , is still holding the patient interface  3000  against the nose to ensure that a proper seal is retained as tension sealing force is released from the strap  3301 .  FIG.  103    shows the patient  1000  adjusting the patient interface  3000  against the nares to ensure a proper fit and seal as well as to locate the rigidiser arms under the cheek bones.  FIG.  104    then shows the patient  1000  with the patient interface  3000  and positioning and stabilising structure  3300  donned and prepared for therapy. 
       FIGS.  105  to  107    show perspective views of the patient  1000  adjusting the patient interface  3000  against the nares to ensure a proper seal by the seal-forming structure  3100 . From  FIG.  105    to  FIG.  107    the patient  1000  can be seen tilting the patient interface  3000  progressively further downward and against the nose to complete the seal against the nose with the seal-forming structure  3100 . These views show the patient  1000  adjusting the patient interface  3000  with one hand, although it should be understood that the patient interface  3000  could be located and adjusted with two hands. 
       FIGS.  108  to  112    show a series of rear views of a patient  1000  adjusting the positioning and stabilising structure  3300  against the back of the head.  FIG.  108    shows the positioning and stabilising structure  3300  resting against back of the head. The strap  3301  will have its largest amount of tension sealing force in this position.  FIG.  109    then shows the patient  1000  grasping the upper back strap portion  3317   a  with one hand and the lower back strap portion  3317   b  with the other hand and pulling these back strap portions  3317   a ,  3317   b  apart at the split region  3326 . It should be understood that by pulling these back strap portions  3317   a ,  3317   b  apart that the tension sealing force in positioning and stabilising structure  3300  is decreasing from the position shown in  FIG.  108    because the back strap portions  3317   a ,  3317   b  are becoming nearer to the patient interface  3000 , which is resting in a constant position against the nares. By moving the back strap portions  3317   a ,  3317   b  closer to the patient interface  3000 , the stretched length of the strap  3301  is decreased thus decreasing its tension sealing force.  FIG.  110    is similar to  FIG.  109   , however in this view the patient  1000  has pulled the upper back strap portion  3317   a  and the lower back strap portion  3317   b  further apart. It should be understood that the tension sealing force in the positioning and stabilising structure  3300  has decreased further due to the spreading of the back strap portions  3317   a ,  3317   b .  FIG.  111    shows a further view of the patient  1000  spreading the upper back strap portion  3317   a  and the lower back strap portion  3317   b  apart. Tension sealing force will be decreased again from the position shown in  FIG.  110   . Also, at this point the patient  1000  has nearly completed adjustment of the positioning and stabilising structure  3300  to the desired level of tension sealing force. The upper back strap portion  3317   a  may be located near the top of the head and the lower back strap portion  3317   b  may be located near or below the occipital lobe.  FIG.  112    then shows the patient  1000  with the positioning and stabilising structure  3300  fully adjusted to a desired level of tension sealing force. Again, the upper back strap portion  3317   a  may be located near the top of the head and the lower back strap portion  3317   b  may be located near or below the occipital lobe. Furthermore, it should also be understood that as the tension sealing force in the positioning and stabilising structure  3300  decreases as the upper back strap portion  3317   a  and the lower back strap portion  3317   b  are pulled apart, θ increases accordingly. Although not indicated in these views θ may be about 0° in  FIG.  108    and it increases through the adjustment sequence. If θ has increased to a maximum of about 180° in  FIG.  112   , then the tension sealing force in positioning and stabilising structure  3300  may be about 40% of the tension sealing force in  FIG.  108   . In another example of the present technology, it may be possible to maintain angle θ at a predetermined value at the initial point of bifurcation of the upper back strap portion  3317   a  and lower back strap portion  3317   b , for example, if the rigidiser arm  3302  extends to the bifurcation point  3324  and splits into upper and lower arms both extending slightly into the back strap portions  3317   a ,  3317   b . This may encourage the patient  1000  to split the back strap portions  3317   a ,  3317   b  to adjust headgear tension. Also, it reinforces the bifurcation point  3324 , for example, using an external seam tape or a plastic clip on the Y-shaped section where a side strap portion  3315 ,  3316  converges with the back strap portions  3317   a ,  3317   b . Such a plastic clip may provide a branding opportunity by pad printing branding and logo information on it. 
     In one form of the present technology, the positioning and stabilising structure  3300  has two points of connection with the frame  3310  and hence there are two rigidiser arms  3302  and a single hollow strap  3301  with split region  3326 . One problem with this type of patient interface  3000  is that the split region  3326  may ride up or down depending on which back strap portion  3317   a ,  3317   b  has more pull. In order to this problem, the split region  3326  that contacts the back of the patient&#39;s head has an even distribution in pull in either direction (top to bottom). Therefore the problem of riding up or down is alleviated. 
     The positioning and stabilising structure  3300  may comprise at least one strap  3301  (see, e.g.,  FIG.  166   ) and at least one rigid element or rigidiser arm  3302  (see, e.g.,  FIG.  19   ). The strap may be made of an elastic material and may have elastic properties. In other words, the strap  3301  may be elastically stretched, e.g., by a stretching force and, upon release of the stretching force, returns or contracts to its original length. The strap  3301  may be made of or comprise any elastomeric material such as elastane, TPE, silicone etc. The strap material may also represent a combination of any of the above materials with other materials. The strap  3301  may be a single layer or multilayer strap. The sides of the strap  3301 , particularly the sides for contacting the patient during use, may be woven, knitted, braided, molded, extruded or otherwise formed. This may be achieved by the strap  3301  being made of or comprising a layer of a material exhibiting the respective properties. The strap  3301  may comprise or is made of a textile material such as a woven material. Such material may comprise artificial or natural fibers for, on the one hand providing desired and beneficial surface properties such as tactile properties. On the other hand, the strap material may include elastomeric material for providing the desired elastomeric properties. 
     In the  FIGS.  65  to  145   , the strap  3301  is shown as being one individual strap for being attached, directly or via the frame  3310 , to a seal-forming structure  3100 . However, it may be appreciated that the strap  3301  may comprise multiple individual straps which are or may be connected to one another. Adjustment may be provided, however, by varying where the strap is secured to a patient interface or other rigid elements such as a connector. In addition or alternatively, adjustment could be allowed by adding a mechanism, such as slide over ladder lock clips on the back or side straps (as shown, e.g., in  FIGS.  75 ,  76  and  166   ) or by otherwise adjusting the elastic length of the strap  3301  and positioning and stabilising structure  3300 , respectively. 
     Rigidiser Arm  3302   
     As can be seen in  FIGS.  19  and  166   , an example of the present technology may comprise stiffened headgear to retain the patient interface  3000  on the patient  1000 . As shown in the drawings depicting this example, the positioning and stabilising structure  3300  may contain at least one rigidiser arm  3302 . 
     In the present example of the technology, the seal-forming structure  3100  of the patient interface  3000  is retained in a desired position on the underside of the nose of the patient  1000  by the support of rigidiser arms  3302 . The positioning and stabilising structure  3300  may locate the patient interface  3000  such that it does not contact the patient  1000  except at the seal-forming structure  3100 . 
     In certain prior art examples the patient interface may be designed to at least partially rest against the upper lip of the patient and in doing so the face of the patient&#39;s upper lip provides a measure of support to retain the patient interface in a desired location, as described in U.S. Pat. No. 7,900,635. In the present example, however, it is desired that the patient interface  3000  not rest against the upper lip of the patient  1000 , as can be seen in  FIGS.  18  and  19   . Particularly,  FIG.  19    shows the posterior wall  3220  of the plenum chamber  3200  is shown separated from the septum and/or upper lip of the patient  1000  by a gap or spacing S. This arrangement has the advantage of preventing irritation or injury to the patient  1000  at the septum and/or upper lip by contact and friction with the posterior wall  3220  of the plenum chamber  3200  during extended periods of wear. Avoidance of concentrated pressure on certain locations of the septum and/or the upper lip can prevent skin breakdown and sores from forming. 
     The arrangement of this particular example, wherein the patient&#39;s septum and/or upper lip is separated from the posterior wall  3220  of the plenum chamber  3200  is accomplished by rigidiser arm  3302 , as can be seen in  FIGS.  19  and  166   . As shown in  FIG.  19   , the rigidiser arm  3302  of the positioning and stabilising structure  3300  may be supported against the cheek of the patient  1000 , approximately above the nasolabial sulcus (see  FIG.  2   c   ). The rigidiser arm  3302  of the positioning and stabilising structure  3300  may be formed with a predetermined curve at the curved profile  3323  to approximate the curve of the patient&#39;s corresponding cheek region until the patient&#39;s cheekbone. The rigidiser arm  3302  may extend across a substantial portion of the cheek region from the point of connection with the frame  3310  until the distal free end  3302 . 1  of the rigidiser arm  3302 . The distance between the point of connection with the frame  3310  until the distal free end  3302 . 1  of the rigidiser arm  3301  is about 120 mm. Rigidiser arm  3302  may extend at an angle, e.g., approximately a right angle, away from the patient&#39;s face and substantially parallel to the nasal ala. In other words, an inner surface of the main section  3333  of the rigidiser arm  3302 , in particular, the curved profile  3323  contacts and extends across a substantial portion of the patient&#39;s cheek region. This contact results in the locating and locking the patient interface  3000  on the patient&#39;s face at semi-fixed position. This contact minimises any vertical movement of the rigidiser arms  3302  relative to the patient&#39;s face. Also, at least a region of the curved profile  3323  proximal to the sharp bend  3307  is intended to maintain contact with the patient&#39;s cheekbone or cheek. When the patient  1000  lies with one side of their face against a bed pillow, the force exerted against the rigidiser arm  3302  and/or some of the extension  3350  or flexible joint  3305  on the bed pillow is minimised or prevented from transmitting to the other rigidiser arm because the sharp bend  3307  and extension  3350  of that rigidiser arm  3302  largely absorb such a force before affecting the seal with the patient&#39;s airways. In other words, lateral force acting upon the positioning and stabilising structure  3300  is at least partially decoupled because the region of the curved profile  3323  is in contact with the patient&#39;s cheek and there is some absorption of this force by the extension  3350  or flexible joint  3305 . 
     Rigidiser arm  3302  may also provide a supported decoupling of the patient interface  3000 , such that the patient interface  3000  may be located in a desirable position at the underside of the patient&#39;s nose with the tension forces of positioning and stabilising structure  3300  retaining the patient interface  3000  in position not causing undesirable contact of the patient interface  3000  against the septum and/or upper lip. Furthermore, the rigidiser arm  3302  may be dimensioned such that the posterior wall  3220  is distance from the patient&#39;s septum and/or upper lip by spacing S. Additionally, the tension of the positioning and stabilising structure  3300  is transmitted primarily to the patient&#39;s cheeks across the width and breadth of rigidiser arm  3302  and not against inwardly towards the face of the patient  1000  against the nose. This exemplary arrangement is advantageous because using the tissue of the cheeks, a relatively large region of the face, to dissipate retention forces may afford the patient greater comfort, as opposed to using the patient&#39;s nose and/or upper lip, which may be more sensitive due to its cartilaginous nature. This exemplary arrangement also allows the seal-forming structure  3100  to be retained with an amount of force sufficient to create a seal against the patient&#39;s airways at the underside of the patient&#39;s nose, while not allowing the retention force to rise to the level of causing discomfort to the patient  1000 . 
     It may be desirable to avoid contact between the rigidiser arms  3302  and the plenum chamber  3200 . Thus, the plenum chamber  3200  may be made sufficiently wide so as to avoid contact with the rigidiser arms  3302 . 
     Stretching of Headgear Strap Relative to Rigidiser Arm 
     In the example shown in  FIG.  166   , two rigidiser arms  3302  are inserted into right and left side strap portions  3315 ,  3316  of the strap  3301  of the positioning and stabilising structure  3300 , the rigidiser arm  3302  is held in place by the surrounding strap  3301  while at the same time a sleeve-like configuration of strap  3301  allows at least a portion of the strap to stretch or move relative to the rigidiser. The rigidiser arm  3302  cannot be seen in this view as it is contained within the strap  3301 . 
     The attachment of the strap  3301  to the rigidiser arm  3302  described in the preceding section may also effect the size of head that the positioning and stabilising structure  3300  may accommodate. In other words, by providing a greater length of strap  3301  along the rigidiser arm  3302  it may be possible to increase the total stretchable length of the positioning and stabilising structure  3300  such that even larger heads may be accommodated without needing to increase the stretchability of the strap. Furthermore, it may be possible to vary, along the length of the rigidiser  3302 , where the strap  3301  is connected. This would allow for an even greater range of head sizes to be accommodated without 
     The rigidiser arm  3302  may thus be allowed to move generally unrestrictedly along the length of the sleeve, attached to the sleeve  3301 , or may be adjacent to one of its ends. 
     Split Back Straps of Positioning and Stabilising Structure 
     According to one aspect, the structure of strap  3301  and positioning and stabilising structure  3300  is of advantage. In particular, as  FIG.  166    depicts, the provision of two elastic straps or strap portions  3317   a ,  3317   b  at the back allows the head to be cupped and the tension vector(s) to be adjusted by suitably positioning them, e.g. by spreading. The provision of two back strap portions  3317   a  and  3317   b  also allows better support and stability, as well as increased flexibility in avoiding specifically sensitive regions of the back of the head. 
     The two smaller straps or strap portions  3317   a ,  3317   b  at the back of the head may be equal in length and not adjustable except through the elasticity of the material or through increasing both in tightness equally by shortening the total length at the arms of the positioning and stabilising structure. For example, a sliding mechanism (not shown) may be provided that allows the straps to be overlapped to a different extent, thus changing the overall length of the positioning and stabilising structure  3300 . 
     As indicated above, two or more joints could be provided creating the positioning and stabilising structure  3300  from three, four or more separate straps rather than strap  3301  being one continuous piece. This might complicate the assembly, but may simplify the manufacturing process. Joints may be placed at the bifurcation or Y-junction between the side strap portions  3315 ,  3316  and two back strap portions  3317   a ,  3317   b  or cantered at the back. The joints may be sewn, welded, glued, or over molded and could incorporate a high friction material to help reduce movement on the head. 
     In one example of the present technology, one or more threads of the strap  3301  may consist of an adhesive or glue. After the strap  3301  is manufactured with this thread, heat is applied to the strap  3301  causing the adhesive or glue thread to melt to reinforce the strap  3301  in areas at or proximal to the adhesive or glue thread. 
     High friction materials may also be added to the inside surface of the back and side strap portions  3315 ,  3316 ,  3317   a ,  3317   b , to reduce the straps slipping. For the arms or side strap portions  3315 ,  3316  this would help the positioning and stabilising structure  3300  stay on the cheeks and at the back strap portion  3317  it could stop the positioning and stabilising structure  3300  from sliding across the back of the head. Such material may be printed, cast or molded onto the surface or incorporated into joints, sewing or welding processes as mentioned above. 
     The split region  3326  at the back of the patient&#39;s head may include two, three or more straps  3317   a ,  3317   b  for stability. A positioning and stabilising structure  3300  similar to the described, may be used with full face (one or more seals for the nose and mouth) or nasal masks also. 
     It is possible that the maximum distance permitted between the back strap portions  3317   a ,  3317   b  may be limited or constrained to prevent the back strap portions  3317   a ,  3317   b  being split apart completely or split beyond a predetermined distance. A joining strap across the split region  3326  or netting across the split region  3326  may be connected to the back strap portions  3317   a ,  3317   b  to limit their ability to split apart beyond a predetermined distance. 
     The Connection Between a Mask Frame and a Rigidiser Arm 
     According to examples of the present technology to be described in greater detail below in reference to  FIGS.  35  to  64   , the patient interface  1000  may include a mask frame  3310  and a rigidiser arm  3302 . As will become apparent from the following description the rigidiser arm  3302  may function to direct the vector of tension generated by a strap  3301  or straps of the positioning and stabilising structure  3300  in a desired direction so as to ensure effective sealing of the seal-forming structure  3100  against the patient&#39;s airways, while directing straps  3301  of the positioning and stabilising structure  3300  away from the patient&#39;s eyes and line of sight. Thus, it should also be understood that the rigidiser arm  3302  and the mask frame  3310  must be formed and connected to facilitate an effective direction of the sealing force. It may be advantageous to allow the rigidiser arm  3302  to flex relative to the mask frame  3310  to accommodate the various shapes and sizes of patients&#39; faces and heads. To improve patient comfort, the direction and degree of flexing between the rigidiser arm  3302  and the mask frame  3310  may be specifically controlled. A flexible joint  3305  may accomplish this or the rigidiser arm  3302  may be directly connected to the mask frame  3310 . 
     A Flexible Joint to Connect a Rigidiser Arm and a Mask Frame 
     Referring to  FIGS.  35  to  38   , a patient interface  3000  is provided generally comprising a mask frame  3310 , a rigidiser arm  3302  and a flexible joint  3305 . A retaining structure  3242  may be removably detachable with the mask frame  3310 . The retaining structure  3242  may hold a seal-forming structure  3100  on the mask frame  3310 . The rigidiser arm  3302  may be made from a thermoset or thermoplastic. For example, Hytrel® 5556 manufactured by DuPont™ is a thermoplastic polyester elastomer which exhibits excellent creep resistance and may be used as the material for the rigidiser arm  3302 . The rigidiser arm  3302  may be part of a positioning and stabilising structure  3300  to locate and retain the mask frame  3310  in position on a patient&#39;s face for delivery of respiratory therapy. In one example, the positioning and stabilising structure  3300  has two rigidiser arms  3302  at its distal ends. Each rigidiser arm  3302  may be permanently connected to opposite sides of the mask frame  3310 . 
     An elastic fabric strap  3301  may be slipped over each rigidiser arm  3302  to form the positioning and stabilising structure  3300  as disclosed, for example, in U.S. Provisional Application No. 61/676,456, filed Jul. 27, 2012, which is incorporated by reference herein in its entirety. The elastic fabric strap  3301  may extend around the head of the patient  1000  and may be bifurcated to provide self-adjustment. The rigidiser arm  3302  may also include a protruding end  3306  that retains a pocketed end of the elastic fabric strap  3301 . In an example, the rigidiser arm  3302  is inserted through a button-hole proximal to the pocketed end and into the hollow elastic fabric strap  3301 . When the elastic fabric strap  3301  is stretched as the patient interface  3000  is donned, the direction of stretch and headgear tension vector of the elastic fabric strap  3301  is guided by the shape and profile of the rigidiser arm  3302 . The protruding end  3306  is a fixed anchor at the base of the rigidiser arm  3302  proximal to the mask frame  3310  and provides the starting point for the stretch of the elastic fabric strap  3301 . The protruding end  3306  permits the elastic fabric strap  3301  to be connected and disconnected from the rigidiser arm  3302  to facilitate washing of the elastic fabric strap  3301  separately from the mask frame  3310  and rigidiser arms  3302 . The rigidiser arm  3302  also frames the face by keeping the elastic fabric strap  3301  away from the eyes and over the ears which leads to the patient interface  3000  being perceived as unobtrusive by the patient. The rigidiser arm  3302  may be generally a planar arm of a predetermined thickness. The thickness of the rigidiser arm  3302  may vary along its length and may be about 1 mm at a distal free end  3302 . 1  and gradually increases in thickness to 1.5 mm along the curved profile  3323  until the distal portion of the rigidiser arm  3302  proximal to the point of connection with the flexible joint  3305 . Since the distal free end  3302 . 1  has less material relative to the other areas of the rigidiser arm  3302  there is a tendency for any flexing of the rigidiser arm  3302  to occur on or proximal to the distal free end  3302 . 1  first before other areas of the rigidiser arm  3302  start to flex. The order of flexing is intended to improve comfort because the distal free end  3302 . 1  is close to the patient&#39;s ears, cheekbones and temples which can be a particularly sensitive region of the face and conformity and less resistance to bending and deformation may be required. A sharp bend  3307  may be provided at a distal portion of the rigidiser arm  3302  proximal to the point of connection with the flexible joint  3305 . The sharp bend  3307  may be at an angle of substantially 90 degrees or less. The sharp bend  3307  may also provide increased rigidity to fix the rigidiser arm  3302  in position relative to the mask frame  3310 . The sharp bend  3307  may prevent or minimise stretching in a longitudinal direction. Also, the sharp bend  3307  may accommodate compression of the rigidiser arm  3302 . If a force is applied to the side of a rigidiser arm  3302  in the coronal plane, the majority of the flexing may occur at or proximal to the sharp bend  3307 . 
     The flexible joint  3305  may be provided between the rigidiser arm  3302  and the mask frame  3310 . The flexible joint  3305  may be made from thermoplastic elastomer (TPE) which provides high elastic properties. For example, a Dynaflex™ TPE compound or Medalist® MD-115 may be used. The mask frame  3310  may be made from polypropylene (PP) material. PP is a thermoplastic polymer with good resistance to fatigue. An advantage of the flexible joint  3305  may be that it enables the rigidiser arm  3302  and the mask frame  3310  to be permanently connected to each other. Hytrel® and PP cannot be integrally bonded to each other by forming covalent or hydrogen bonds. Integrally bonded includes chemically bonded but without the use of an added adhesive substance. In an example, the rigidiser arm  3302  is provided with a protrusion  3309  that extends outwardly from the distal portion of the rigidiser arm  3302 . Turning to  FIG.  38   , the inner side  3318  of the protrusion  3309  is the surface of the rigidiser arm  3302  that the protrusion  3309  extends from. An outer exposed side  3319  of the protrusion  3309  is opposite the inner side  3318  (see  FIG.  38   ). The protrusion  3309  may have a void  3320  in a central region of the protrusion  3309 . The void  3320  may extend substantially vertically through the protrusion  3309  from a top side  3321  to a bottom side  3322  of the protrusion  3309 , and may be enclosed around its perimeter by the protrusion  3309 . The outer side  3319  may be a substantially planar surface that extends beyond the protrusion  3309 . When viewed from above, the protrusion  3309  may have a generally T-shaped cross section with the void  3320  visible in the central region. The protrusion  3309  may also serve to retain the elastic fabric strap alternatively or in addition to the protruding end  3306 . 
     Another advantage of the flexible joint  3305  may be that it is relatively more flexible than the rigidiser arm  3302 . This flexibility may be provided by the combination of the TPE material and also the structural features of the flexible joint  3305 . Structurally, the flexible joint  3305  may have a predetermined thickness to enable a predetermined degree of flexing, and also the amount of curvature of the flexible joint  3305  may be selected to contribute to the degree of flexing. The flexible joint  3305  may be able to flex radially on its longitudinal axis relative to the mask frame  3310  but may be resistant to flexing in other directions. This flexibility may provide a self-adjustment function to the patient interface  3000  and may compensate for deviations to facial contours, nose dips or sleeping positions. This flexing may accommodate the anthropometric range of most patients. Greater flexibility may be required at this location compared to the flexibility within the rigidiser arm  3302  itself. Also, since flexing is restricted to a certain direction, stability of the mask frame  3310  may be improved and the position of the mask frame  3310  may be substantially maintained relative to the nose and mouth if the elastic fabric of the positioning and stabilising structure  3300  requires adjustment. 
     The flexible joint  3305  may be overmolded to the mask frame  3310 . PP and TPE can be integrally bonded to each other. In other words, a fusion bond or chemical bond (molecular adhesion) between the flexible joint  3305  and the mask frame  3310  is possible. This may form a permanent connection between the flexible joint  3305  and mask frame  3310 . The flexible joint  3305  may be overmolded to the protrusion  3309  of the rigidiser arm  3302 . TPE and Hytrel® cannot be integrally bonded to each other. However, during overmolding in accordance with an example of the present technology, the TPE material for the flexible joint  3305  flows into the void  3320  of the protrusion  3309  and around the protrusion  3309 . TPE material surrounds the front and rear sides and the top and bottom sides  3321 ,  3322  of the protrusion  3309 . Consequently, a mechanical interlock may be provided to form a permanent connection between the flexible joint  3305  and the rigidiser arm  3302 . The outer side  3319  of the protrusion  3309  may be flush with the outer surface of the flexible joint  3305 . This is visually aesthetically pleasing. 
     Referring to  FIGS.  42  to  46   , in another example, at the distal end of the rigidiser arm  3302  may be an extension  3350 . The extension  3350  may project from the outer surface of the rigidiser arm  3302  via a stem  3361 . The extension  3350  may be L-shaped when viewed from above. The extension  3350  may have a sharp bend  3307  of approximately 90 degrees which separates a first section  3363  from a second section  3364  of the extension  3350 . The first section  3363  may be oriented in a plane that is parallel to the outer surface of the rigidiser arm  3302  at the distal end. The end  3363 A of the first section  3363  may have curved corners. The second section  3364  may have a height and thickness that is less than the first section  3363 . Therefore the top and bottom edges of the second section  3364  may be set back from the top and bottom edges of the first section  3363 . The rigidiser arm  3302  may also include a protruding end  3306  that retains a pocketed end  3311  of the elastic fabric strap  3301 . The stem  3361  may also serve to retain the elastic fabric strap alternatively or in addition to the protruding end  3306 . 
     The second section  3364  may have a first protrusion  3365  and a second protrusion  3366 . The protrusions  3365 ,  3366  may extend laterally in an outwardly direction from the rigidiser arm  3302 . Adjacent to the first protrusion  3365  may be a first slot  3367  and adjacent to the second protrusion  3366  may be a second slot  3368 . The slots  3367 ,  3368  each may provide a void through the thickness of the second section  3364  and may have approximately the same height as the protrusions  3365 ,  3366 . 
     A flexible joint  3305  made from TPE may be overmolded to the second section  3364  of the extension  3350  of the rigidiser arm  3302 . During overmolding, TPE material may flow through the slots  3367 ,  3368  and surround the protrusions  3365 ,  3366 . The majority of the second section  3364  may be enclosed by the TPE material of the flexible joint  3305 . This may provide a mechanical interlock which enables the flexible joint  3305  to be permanently connected to the rigidiser arm  3302 . Since the second section  3364  may have a height and thickness that is less than the first section  3363 , the TPE material overmolded to the second section  3364  may not excessively protrude beyond the first section  3363 . The flexible joint  3305  may also be overmolded to the mask frame  3310  to connect the flexible joint  3305  and the rigidiser arm  3302  thereto. 
     Similar to the previously described example, greater relative flexibility may be provided by the flexible joint  3305  relative to the rigidiser arm  3302 . Flexing in this location and the control of the direction of flexing, may accommodate the anthropometric range of most patients and maintains stability of the patient interface  3000  in use. 
     A Direct Connection Between a Rigidiser Arm and a Mask Frame 
     Referring to  FIGS.  39  to  41   , in another example, a flexible joint  3305  made from TPE may not be required. An extension  3350  may be used. The rigidiser arm  3302  may have a main body or main section  3333  comprising the curved profile  3323  and sharp bend  3307 . The rigidiser arm  3302  may also include a protruding end  3306  that retains a pocketed end of the elastic fabric strap. Along a majority of its longitudinal axis, a curved profile  3323  may be shaped to correspond to an obtuse angle to closely follow the contour of the face of a patient. At the distal end of the rigidiser arm  3302 , an extension  3350  may be provided after the sharp bend  3307 . The extension  3350  may project outwardly from the rigidiser arm  3302  in the coronal plane. A recess  3329  (see  FIGS.  40 ,  50 ,  57 ,  58   ) may be defined in a surface of the rigidiser arm  3302  at the point the extension  3350  projects from the rigidiser arm  3302 . The height of the extension  3350  may be less than the height of the main section  3333  of the rigidiser arm  3302 . This may enable greater flexibility for the extension  3350  compared to the main section  3333  of the rigidiser arm  3302  because of a relative reduction of material for the extension  3350  relative to the rigidiser arm  3302 . The rigidiser arm  3302  including the extension  3350  may be made from Hytrel®. Hytrel® provides the rigidiser arm  3302  with a flexural modulus of 180 MPa at 23° C. and a tensile modulus of 180 MPa ( 26 ). The enclosable section  3354  of the extension  3350  may be overmolded by the PP material of the mask frame  3310  at the edge of the mask frame  3310 . This is performed in-mold and during overmolding, the PP material of the mask frame  3310  may surround the inner, outer, top and bottom surfaces of the enclosable section  3354  to permanently connect the rigidiser arm  3302  with the mask frame  3310  via a mechanical interlock. The encapsulation of the enclosable section  3354  of the extension  3350  by the PP material of the mask frame  3310  provides a mechanical retention without an integral bond between the rigidiser arm  3302  and the mask frame  3310 . 
     The connection between the rigidiser arm  3302  and the mask frame  3310  is a hinged connection at or proximal to bend  3352 . In other words, the rigidiser arm  3302  is able to pivot relative to the mask frame  3310 . The position of the pivot point as far forward as possible in line with the nasal pillows and nares of the patient  1000  to cater for varying nose droop and minimize the moment arm and tube drag caused by the air circuit  4170 . The flexing and rotational movement of the rigidiser arm  3302  relative to the mask frame  3310  in the coronal plane is to accommodate various head widths without excessive force, preferably, less than 1 or 2 Newtons, required to minimise or eliminate pinching of the patient&#39;s cheeks between the two rigidiser arms  3302 . The distance between the two bends  3352  is about 62 mm. This spacing between the between the two bends  3352  avoids the protruding end  3306  of the rigidiser arms  3302  and extension  3350  or flexible joint  3305  touching the patient&#39;s nose proximal to the nose tip and side of the patient&#39;s nose. These areas of the patient&#39;s face may be particularly sensitive so avoidance of contact in these areas may improve comfort. 
     As the patient interface  3000  is donned, the rigidiser arms  3302  may be spread outwardly to accommodate various head widths. Pivoting of the rigidiser arm  3302  relative to the mask frame  3310  will occur as well as flexing of the rigidiser arm  3302  along its longitudinal axis. 
     Additional Features and Examples of the Present Technology 
     In another example the rigidiser arm  3302  may be relatively more resiliently flexible than the mask frame  3310 . The rigidiser arm  3302  may also be formed so as to be flexible only horizontally, i.e., in a plane parallel to the Frankfort horizontal and the transverse plane. Moreover, the rigidiser arm  3302  may not be flexible in a vertical direction, i.e., in a plane perpendicular to the Frankfort horizontal. In other words, the rigidiser arm  3302  is more flexible in a plane parallel to the Frankfort horizontal and the transverse plane and less flexible in any other plane (preferably, not flexible). Furthermore, material of the rigidiser arm  3302  may not be stretchable or extensible. If the rigidiser arm  3302  is stretched at its ends, the curved profile of the rigidiser arm  3302  flattens. These features alone or in combination with shape and dimension may allow the rigidiser arm  3302  to flex and/or frame the face of the patient  1000  without riding or flexing up across or down against the patient&#39;s ears. In turn, this enables the elastic fabric strap  3001  to navigate above the patient&#39;s ears proximal to the Otobasion superior. 
     In the example shown in  FIGS.  35  to  38   , indicia such as a corporate logo may be provided on the outer surface  3319  of the protrusion  3309  to conceal the location of the mechanical interlock. In the example shown in  FIGS.  39  to  41   , the indicia may be provided on an outer surface  3355  of the extension  3350 . The indicia may visually assist the patient in determining the correct orientation of the patient interface  3000  when donning the patient interface  3000 , to prevent it from being donned upside down. If the indicia are also a raised/embossed surface, this may provide tactile feedback for the patient  1000  especially if they are donning the patient interface  3000  in a darkened environment. 
     In a further example, an adhesive accelerator may be used after surface treatment to permanently connect the rigidiser arm  3302  to the mask frame  3310 , or to permanently connect the rigidiser arm to the flexible joint  3305 . In this example, a mechanical interlock is not necessary. 
     In another example, the rigidiser arm  3302  is made from a material that can be integrally bonded with the mask frame  3310  made from PP material. The rigidiser arm  3302  may be made from a fiber reinforced composite PP material, for example, Curv® manufactured by Propex Inc. Curv® has a similar level of resilient flexibility as Hytrel®. Curv® is provided in sheet form, and requires laser cutting into the desired shape of the rigidiser arm  3302 . To obtain the desired thickness for the rigidiser arm  3302 , compression or layering of sheets may be performed to adjust the thickness of the rigidiser arm  3302  in certain areas. Since Curv® is made from the same material as the mask frame  3310 , an integral bond is possible when the rigidiser arm  3302  is overmolded to the mask frame  3310 . 
     The patient interface  3000  may include a nasal cradle as disclosed, for example, in U.S. Provisional Application No. 61/823,192, filed May 14, 2013, which is incorporated herein by reference in its entirety. Nasal pillows may be releasably engageable with the mask frame  3310 . After the rigidiser arms  3302  are permanently connected to the mask frame  3310 , the elastic fabric strap of the positioning and stabilising structure  3300  may be slipped over the rigidiser arms  3302  and secured to the rigidiser arms  3302 . 
     Although a T-shaped protrusion  3309  has been described, it is envisaged other shapes and forms are possible, including a mushroom shaped protrusion, to permanently connect the rigidiser arm  3302  (via a flexible joint in one example) mechanically to the mask frame  3310 . Although a void  3320  has been described, it is envisaged that the protrusion  3309  may not have a void but rather recesses or slots to retain the flexible joint  3305  or mask frame  3310  to the rigidiser arm  3302 . 
     It is envisaged that it is possible to reverse the described connection arrangement and provide the protrusion extending from the mask frame  3310  or flexible joint  3305  rather than rigidiser arm  3302 . In such an example the rigidiser arm  3302  would be overmolded to the flexible joint  3305  or the mask frame  3310 . 
     It is envisaged that the flexible joint  3305  can be permanently connected to the mask frame  3310  without an integral bond. For example, a mechanical interlock may be provided to permanently connect the flexible joint  3305  to the mask frame  3310 . 
     Although the rigidiser arm  3302 , flexible joint  3305  and mask frame  3310  have been described as permanently connected to each other, it is envisaged that some or all may releasably detachable from each other using for example, a mechanical clip (snap-fit) assembly. 
     The Shape of a Rigidiser Arm 
       FIGS.  61  to  64    show a rigidiser arm  3302  according to an example of the present technology plotted in two and three dimensions.  FIGS.  61  to  63    show three two dimensional views of a rigidiser arm  3302  according to an example of the present technology plotted on a grid.  FIG.  61    shows the X-Y plane,  FIG.  62    shows the X-Z plane, and  FIG.  63    shows the Y-Z plane. The origin is also indicated in these views for orientation purposes. Numbered coordinates are also shown in each of these and these coordinates may define the curve of the rigidiser arm  3302  in these planes. 
     The following chart lists the coordinates of the profile of the rigidiser arm  3302  shown in these views. It should be understood that each coordinate is numbered consistently across each of the four views. 
     
       
         
           
               
               
               
               
               
             
               
                   
                   
               
               
                   
                 Point # 
                 X 
                 Y 
                 Z 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 1 
                 26.67 
                 14.25 
                 12.76 
               
               
                   
                 2 
                 22.00 
                 26.87 
                 24.92 
               
               
                   
                 3 
                 27.30 
                 28.57 
                 26.37 
               
               
                   
                 4 
                 37.94 
                 32.84 
                 30.10 
               
               
                   
                 5 
                 46.72 
                 37.84 
                 34.57 
               
               
                   
                 6 
                 59.77 
                 51.55 
                 45.79 
               
               
                   
                 7 
                 65.02 
                 61.69 
                 52.45 
               
               
                   
                 8 
                 68.36 
                 73.68 
                 56.36 
               
               
                   
                 9 
                 69.09 
                 83.53 
                 55.98 
               
               
                   
                 10 
                 69.78 
                 94.70 
                 54.31 
               
               
                   
                 11 
                 69.06 
                 102.83 
                 54.02 
               
               
                   
                 12 
                 68.69 
                 110.47 
                 55.36 
               
               
                   
                 13 
                 72.25 
                 113.84 
                 51.65 
               
               
                   
                 14 
                 73.00 
                 110.04 
                 49.69 
               
               
                   
                 15 
                 73.70 
                 103.72 
                 48.28 
               
               
                   
                 16 
                 73.81 
                 95.03 
                 48.56 
               
               
                   
                 17 
                 73.26 
                 86.38 
                 49.37 
               
               
                   
                 18 
                 71.54 
                 75.71 
                 48.65 
               
               
                   
                 19 
                 67.84 
                 66.29 
                 44.75 
               
               
                   
                 20 
                 60.55 
                 55.68 
                 36.66 
               
               
                   
                 21 
                 52.68 
                 48.30 
                 29.33 
               
               
                   
                 22 
                 43.87 
                 42.88 
                 23.34 
               
               
                   
                 23 
                 33.65 
                 38.87 
                 18.62 
               
               
                   
                 24 
                 27.58 
                 37.35 
                 16.76 
               
               
                   
                 25 
                 21.65 
                 36.15 
                 15.26 
               
               
                   
                 26 
                 26.67 
                 22.22 
                 2.56 
               
               
                   
                   
               
            
           
         
       
     
       FIG.  64    shows a further view of the rigidiser arm  3302  depicted in  FIGS.  61  to  63    in three dimensions. The X, Y, and Z axes are indicated, as well as the origin, to aid in orientation. 
     The shape of the curve of the rigidiser arm  3302  is intended to closely follow the patient&#39;s cheek. With the elastic fabric strap  1200  covering the rigidiser arm  3302 , the relative position of the rigidiser arm  3302  in contact with the patient&#39;s cheek during use is such that it does not slip on the patient&#39;s face. For example, the rigidiser arm  3302  may sit slightly below the patient&#39;s cheekbone which prevents the rigidiser arm  3302  from sliding upwards. Also, contact between most of or all the inner side surface of the rigidiser arm  3302  and the patient&#39;s face may increase friction to prevent slippage and ultimately minimise disruption of sealing forces. The shape of the curved profile  3323  of the rigidiser arm  3302  directs the positioning and stabilising structure  3300  between the eyes and ears over the majority of the anthropometric range. This orientation is advantageous because it is aesthetic and unobtrusive from the perspective of the patient  1000  and the patient&#39;s bed partner  1100 . When viewed from above, the curved profile  3323  of the rigidiser arm  3302  has a larger radius than the rigidiser arm  3302  when viewed from the side. 
     The Flexibility of a Rigidiser Arm 
     As described earlier and referring to  FIGS.  52  and  55   , the rigidiser arm  3302  is more flexible in certain directions at certain locations along the rigidiser arm  3302 . Flexural stiffness of the rigidiser arm  3302  is compared. For comparative purposes, the flexibility of the rigidiser arm  3302  is measured against rigidised headgear of some prior masks by ResMed Limited in an outwardly lateral direction in the coronal plane and in the inferior vertical direction in the sagittal plane. 
     
       
         
           
               
               
            
               
                   
               
               
                   
                 Newtons of force (N) required  
               
               
                   
                 to displace upper distal tip of  
               
               
                   
                 rigidiser arm by 5 mm 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 Vertical  
                 Laterally  
               
               
                 Mask name 
                 Mask type 
                 Down 
                 Outwards 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 Present Technology 
                 nasal pillows 
                 0.132 
                 0.0143 
               
               
                 ResMed Pixi 
                 paediatric nasal 
                 1.107 
                 0.0356 
               
               
                 ResMed Mirage Swift 
                 nasal pillows 
                 1.15 
                 0.0258 
               
               
                 LT 
                   
                   
                   
               
               
                 ResMed Mirage Swift I 
                 nasal pillows 
                 0.966 
                 0.0647 
               
               
                 ResMed Mirage Vista 
                 nasal 
                 4.35 
                 0.0776 
               
               
                   
               
            
           
         
       
     
     This comparison shows the differences in force (in Newtons) required to displace the upper distal tip of a rigidised headgear component when connected to a mask frame by a distance of 5 mm. Choosing the upper distal tip of a rigidised headgear component as the location to measure is because this location comes into contact with a sensitive facial area and certain types of flexibility provides comfort without compromising seal stability. Measuring the direction of flexibility in an outwardly lateral direction in the coronal plane (laterally outwards) is intended to measure the ability of the rigidiser arm  3302  to accommodate patients with large face widths as shown in  FIG.  52    in broken line. The resilient flexibility of the rigidiser arm  3302  allows the patient interface  3000  to more precisely fit a wider range of facial shapes. For example, the same patient interface  3000  could be used on patients with a narrow angular face (the so-called crocodile shape) as those with a wider flatter face (the so-called panda shape). Measuring the direction of flexibility in the inferior vertical direction in the sagittal plane (vertical down) is intended to measure the ability of the rigidiser arm  3302  to handle tube torque exerted by the air circuit  4170  during therapy as shown in  FIG.  55    in broken line. Both measurements are taken using an Instron machine with a 50N load cell. 
     For measuring the vertical down direction, each mask is secured to a plate and sits level with it and has the rigidised headgear component at an angle that would be normally be on a patient&#39;s face. This plate is fastened to a large circular base plate used for the Instron machine. The rigidised headgear component is held in a jig to prevent twisting and slipping and this jig is manually lowered such that it makes contact with the upper distal tip of the rigidised headgear component. The Instron machine is zeroed at this height position. Next, compression extension of 5 mm is applied at a rate of 50 mm/minute, and the measurements are recorded. 
     For measuring the laterally outwards direction, a spacer and a 90 degree elbow are secured to a first plate. Each mask is secured to a second plate and sits level with it and has the rigidised headgear component at an angle that would be normally be on a patient&#39;s face. A spring clamp is used to fix the second plate with the 90 degree elbow on the first plate such that the first plate is held perpendicular to the second plate. A large prong is used to locate it to the upper distal tip of the rigidised headgear component. The Instron machine is zeroed at this height position. Next, compression extension of 5 mm is applied at a rate of 50 mm/minute, and the measurements are recorded. 
     The measurements show that the rigidiser arm  3302  connected to the frame  3310  is more flexible in both directions by a significant factor. For accommodating large face widths, the rigidiser arm  3302  is 1.8 times more flexible than the second most flexible mask in this direction (ResMed Mirage Swift LT). For accommodating tube torque, the rigidiser arm  3302  connected to the frame  3310 , the rigidiser arm  3302  is 8.39 times more flexible than the second most flexible mask in this direction (ResMed Pixi). By having a more flexible rigidiser arm  3302  when displaced in these directions provides the patient  1000  with greater comfort, less likelihood of seal disruption caused by tube torque and therefore leads to increased patient compliance with therapy in terms of frequency of use and therapy duration. 
     Relative flexibility of the rigidiser arm  3302  in different directions is also an important consideration. If flexibility in the vertical down direction is too high (i.e. equal to the laterally out direction), there may be seal instability. In one example, the rigidiser arm  3302  is more flexible in the laterally out direction than the vertical down direction. The rigidiser arm  3302  is 9 to 10 times more flexible in the laterally out direction than the vertical down direction. Preferably, the rigidiser arm  3302  is about 9.23 times more flexible in the laterally out direction than the vertical down direction. Tube torque may also be addressed in conjunction with other mask components such has the short tube  4180  (e.g. making it lighter weight, more slinky or more flexible) or the use of a swivel connector, ball and socket joint or gusset or pleated section. However, varied facial widths are predominantly addressed by the flexibility of the rigidiser arm  3302  and therefore the rigidiser arm  3302  needs to be more flexible in the laterally out direction compared to the vertical down direction. 
     Some rigidised headgear components of prior masks are more rigid than the frame. Typically, these stiff headgear components use threaded arms and bolts to manually adjust the headgear to fit the patient&#39;s head. Although a flexible frame may improve mask comfort, provide a good seal, minimise inadvertent leak and minimise the risk that headgear straps are too tight for low pressure level for therapy, some difficulty would arise if the flexible frame was needed to be releasably detachable with a seal-forming structure. Seal-forming structures are resiliently flexible so that they form a seal against the patient&#39;s airways. If both the seal-forming structure and frame are of similar flexibility (i.e. very flexible or floppy), it would be difficult for a patient  1000  to engage these two parts together, especially a patient with arthritic hands in a darkened room. 
     Some rigidised headgear components of prior masks are detachable from the frame. Typically this is by way of a snap-fit or clip connection between the rigidiser arm and the mask frame, both of which are rigid and stiff components. This type of hard-to-hard connection between the rigidiser arm and frame may result in less flexibility at the point of connection which means more force is required to flex at this point causing discomfort for patients with larger face widths since a pinching force may be experienced when the rigidiser arms are forced to flex outwardly. Some of these rigidiser headgear components have the hard clip at the distal end of the rigidiser arm for releasable connection with the frame. The hard clip is permanently connected to a headgear strap which may damage a washing machine tub or other laundry items when the headgear is washed in a washing machine. Also, some of these rigidised headgear components tend to require a patient interface with a wider frame which means that the headgear straps commence from the frame position at a larger distance apart from other. The wider frame may have integrally formed lateral arms which are considered part of the frame as they are made from the same material. A wider frame may be perceived by patients  1000  and their bed partners  1110  as more obtrusive and aesthetically undesirable because they cover a larger footprint on the face. In contrast, in one example of the present technology, the rigidiser arm  3302  is made from a material that is more flexible than the frame  33310  but less flexible than the strap  1200 . In other words, the strap  1200  is the most flexible component of the positioning and stabilising structure  3300  as it is made from an elastic fabric. The second most flexible component of the positioning and stabilising structure  3300  is the rigidiser arm  3302  which is made from Hytrel® in one example. The most rigid or stiff component is the frame  3310  which not intended to flex, stretch or bend easily or at all because it is the seal-forming structure  3100  that is meant to form a seal with the patient&#39;s airways by resilient deformation. The differences in flexibility of individual components can control the amount of flexing at certain locations and also determine the order that certain components start to flex when a certain force is applied i.e. tube torque or accommodating a larger face width. The differences in flexibility of individual components may also decouple forces before they can begin to disrupt the seal of the seal-forming structure  3100  in a specific manner or sequence. These factors aim to address the requirements of comfort, stability and provision of a good seal at the same time for a patient interface  3000 . Another advantage of the rigidiser arm  3302  is that the same sized rigidiser arm  3302  may be used for patient interfaces  3000  with different sized seal-forming structures  3100  or different sized headgear straps  3301 . When a rigidiser arm  3302  is flexed inwardly, it is likely to make contact with the sides of patient&#39;s nose first before the making contact with the nasal pillows  3130  and dislodging the seal. Then inward range of movement of the rigidiser arms  3302  is limited by the patient&#39;s nose and therefore disruption of the sealing force by movement in such a direction is minimised or eliminated. 
     Vent  3400   
     In one form, the patient interface  3000  may include a vent  3400  constructed and arranged to allow for the washout of exhaled air (including exhaled carbon dioxide). 
     One form of vent  3400  in accordance with the present technology comprises a plurality of very small holes, in other words, a multi-hole vent. Two or more multi-hole vents may be provided on the frame  3310 . They may be located on both sides of the connection port  3600  for an air circuit  4170 . These holes may be the interspaces between the fibers of a textile material. Alternatively, these holes may be microholes (1 micron or less) defined in a substrate of a semi-permeable material using a laser drill operating in the ultraviolet spectral range. Laser drilled microholes may be straight-walled or tapered/trumpet shaped. Another way to create microholes is by using a chemical etchant after masking off areas of the substrate. There may be about 20 to about 80 holes or about 32 to about 42 holes or about 36 to about 38 holes. In one example, if this form of vent  3400  is insert molded, the direction of the holes through the thickness of the vent  3400  may be modified to be skewed rather than perpendicular. This may avoid exhaled air (including exhaled carbon dioxide) blowing directly into the face of a bed partner  1100  if the patient  1000  is facing him or her. In one example, the final number of holes may be determined by blanking off some holes from an original larger number of holes. For example, there may 40 holes and 2 holes are occluded (by filling) so that the final number of holes is 38 holes. The ability to selectively occlude holes both in terms of the quantity and the position of the holes to be occluded provide increased control over the air flow rate and the air diffusion pattern. 
     Referring to  FIGS.  146  to  152   , the patient interface  3000  is a nasal pillows mask and preferably two vents  3400  are located in the plenum chamber  3200  of a mask frame  3310  or specifically located in a cushion clip (that may be preassembled with a cushion) of a mask frame  3310 . A connection port  3600  or short tube  4180  is located between the two vents  3400 . Referring to  FIGS.  153  and  154   , a method for manufacturing a patient interface  3000  for the treatment of respiratory disorders is provided. A porous textile is received ( 51 ) for processing. The method comprises cutting ( 57 ) a vent portion  72 ,  73  from the textile. The textile is formed by interlacing fibers to form an interlaced structure defining tortuous air paths for air to pass therethrough. The textile has a predetermined amount of porosity. The vent portion is held ( 59 ) in a mold. The held vent is permanently connected ( 60 ) to a mask frame  3310 . The vent portion and mask frame  3310  may both be made from a plastic material. This forms a vent  3400  for the patient interface  3000  to washout exhaled air (including exhaled carbon dioxide). 
     Any type of cutting tool  67  may be used to cut the vent portion  72 ,  73  from the textile  65 , for example, a laser or mechanical cutter. More than one vent portion can be cut from the textile  65  at the same time, and preferably two vent portions are cut to form two vents at the same time. If two are cut from roughly the same region of the textile  65 , the airflow rate and material properties of the two vent portions may sometimes be substantially similar. This assists in determining and locating defective material that has been supplied and also reduces the amount of calibration for equipment to adjust the airflow rate if required. In another example, where heat staking by a staking punch  68  is required, rather than cutting the vent portion  72 ,  73  before heat staking, the vent portion  72 ,  73  can be cut from the textile  65  after heat staking. In such a scenario, the first cutting by the cutter  67  can be eliminated. 
     In one example of the present technology, the material of the interlaced fibers is a thermoset or thermoplastic which may include polyester, nylon, polyethylene and preferably polypropylene. In a specific example, the textile  65  may be SEFAR material Tetex Mono 05-1010-K 080 woven polypropylene material. A thermoset may also be used. The textile is typically provided in the form of a roll or ribbon  65  before the cutting step. The weave of the textile  65  is preferably a satin weave. However, other weaves are envisaged including plain weave, plain reverse Dutch weave and twill weave. The textile  65  may also be knitted (e.g. warp knitted) instead of woven. The voids or holes defined by the knit/weave of fibers through the textile  65  do not necessarily have a uniform dimension since there is some variation between the positioning, spacing and compression of the fibers in the weave of the textile. The voids are preferably not straight through holes but rather define a tortuous air flow path between adjacent fibers through the thickness of the textile  65 . A tortuous air flow path may have different pressure regions (higher or lower) along the air path. A tortuous air flow path significantly diffuses the air flow and thereby reduces noise. If the voids were straight through holes, then the fibers of the textile  65  may be arranged in the form of a mesh grid or a matrix. Advantageously, the air flow exiting from the vent  3400  is non-linear, avoids laminar flow and a wide plume with turbulent flow is generated. 
     The patient interface  3000  includes nasal mask, full-face mask or nasal pillows. The mask frame  3310  of the patient interface  3000  has at least one vent  3400 , preferably, two vents  3400 . If there are two vents  3400 , a left vent is positioned on the left side of the anterior surface of the mask frame  3310  and a right vent is positioned on the right side of the anterior surface of the mask frame  3310 . The left and right vents  3400  are separated by an aperture or connection port  3600  for receiving a short tube  4180  operatively connected to a PAP device  4000 . Alternatively, a single continuous vent  3400  positioned in the center of the mask frame  3310  is possible and the short tube  4180  is connected to a side of the mask frame  3310 . The single continuous vent  3400  may have a superficial surface area equivalent to the combined superficial surface area of two vents  3400 . 
     In an example where two or more vents  3400  are provided to the mask frame  3310 , the total or average airflow rate through all the vents  3400  is used to obtain the desired airflow rate by selecting vent portions with different airflow rates. For example, a first vent portion with a low airflow rate may be used with a second vent portion with a high airflow rate. The two vent portions combined may then provide an average airflow rate that is the desired airflow rate. 
     The vent portion is cut or removed from the textile by laser cutting, ultrasonic cutting or mechanical cutting or heat cutting (using a hot anvil). Laser, ultrasonic and heat cutting because they cut and fuse the peripheral edge of the vent  3400  to eliminate stray fibers with loose ends at the peripheral edge of the vent  3400 . A laser cutter  69  can be used for laser cutting. Laser, ultrasonic and heat cutting also assists with subsequent overmolding because it flattens the peripheral edge of the vent and makes it easier to overmold compared to an uneven edge. Consequently, trapped air bubbles are avoided at the bonding location between the vent  3400  and mask frame  3310 , resulting in the mask frame  3310  with the integrated vent  3400  being highly visually appealing and structurally reliable. 
     The permanent connection can be obtained by molecular adhesion using overmolding, co-injection molding or two shot (2K) injection molding. This produces an integral bond and is strengthened when the materials of the vent portion with the mask frame  3310  interact by forming covalent bonds or hydrogen bonds. Some molds allow previously molded parts to be reinserted to allow a new plastic layer to form around the first part. This is referred to as overmolding. The overmolding process involves the use of two materials to form one cohesive component. There are two types of overmolding: insert and “two-shot (2K)”. 
     Two-shot or multi-shot molds are designed to “overmold” within a single molding cycle and must be processed on specialized injection molding machines with two or more injection units. This process is actually an injection molding process performed twice. A high level of molecular adhesion is obtained. The method for manufacturing a patient interface  3000  as described may be performed by overmolding the vent portion of textile to the mask frame  3310 . The vent portion is held in a mold  70  and a molding machine  71  overmolds the vent portion to the mask frame  3310 . Since the textile  65  and mask frame  3310  are preferably made from the same plastic material, overmolding performs a fusion of material between the vent portion of textile and mask frame  3310  which is structurally strong and a permanent bond. In the final assembled patient interface  3000 , it is virtually undetectable by the unaided human eye that the vent  3400  and mask frame  3310  are two distinct parts. 
     The vent  3400  has a maximum cross-sectional width of about 16 mm to about 21 mm, preferably, 18.2 to 18.6 mm, and a maximum cross-sectional height of about 19 mm to about 25 mm, preferably, 21.6 mm to 22 mm, and a thickness of about 0.36 mm to about 0.495 mm, preferably, 0.40 to 0.45 mm. Therefore the superficial area of two vents  3400  is about 800 mm 2 . The superficial area of the porous region of the vent  3400  may be about 201.6 mm 2  to about 278.6 mm 2 , preferably, 240 mm 2 . Therefore, for two vents  3400  the superficial area of the porous region is about 480 mm 2  to 500 mm 2 . The anterior side of the mask frame  3310  has a superficial area of about 1800 mm 2 . The superficial area of the vents  3400  comprises at least 35% of the superficial area of the anterior side of the mask frame  3310 . Preferably, the two vents  3400  comprise 40% to 60% of the anterior side of the mask frame  3310 . Preferably, the two vents  3400  comprise 45% to 55% of the anterior side of the mask frame  3310 . More preferably, the two vents  3400  comprise about 50% of the anterior side of the mask frame  3310 . The interlaced fibers of the vent  3400  provide a semi-rigid woven structure which it to form a significant area of the anterior surface of the mask frame  3310 . The vent  3400  has sufficient rigidity that is able to support its own weight under gravity and does not fold over itself when there is tube torque, and is not floppy. Some prior masks with a vent made of loose fabric cannot maintain their shape, geometry and profile during breathing cycles of the patient (inhalation and exhalation) and therefore the vent will fold over itself during therapy. When such a prior vent folds over itself, the porous region of the vent is reduced by a percentage in a random manner because the folded over sections may partially or fully occlude the vent at these folded over sections. This leads to insufficient washout of exhaled air (including exhaled carbon dioxide). In contrast, the vent  3400  of the present technology does not fold over itself and therefore can ensure that the porous region of the vent  3400  maintains a substantially constant rate of washout for the exhaled air during breathing cycles of the patient  1000  leading to proper washout of exhaled air (including exhaled carbon dioxide) during therapy. 
     In one example, the airflow rate of the vent portion of the textile  65  is first measured ( 52 ) by an airflow meter  66 . A determination ( 53 ) is made on whether there is a difference between the measured airflow rate and a desired airflow rate. If the airflow rate through the vent portion exceeds ( 56 ) a predetermined range, the amount of porosity of the vent portion is selectively reduced ( 54 ). The desired predetermined range is about 42 to about 59 liters per minute at 20 cm H 2 O pressure, preferably, about 47 to about 55 liters per minute at 20 cm H 2 O pressure. For example, the airflow rate through the SEFAR material Tetex Mono 05-1010-K 080 woven polypropylene material may be about 37 to about 64 liters at 20 cm H 2 O pressure, preferably, about 42 to about 58 liters at 20 cm H 2 O pressure. The variance over the length of the textile may be sinusoidal over the length of the textile ribbon. Different areas of the textile when first received from a textile manufacturer may exhibit different air flow rates due to the manufacturing process but not limited to calendering without even heat and force distribution. After the porosity of the vent portion has been reduced, the airflow rate is measured ( 55 ) again for verification to confirm it is now within the predetermined range. The average diameter of the opening of the voids is preferably less than 0.1 mm, and preferably provide a total open area (porous region) of approximately 1% to 10% of the superficial area of the vent  3400 . For example, the total open area (porous region) may be 22 mm 2  where the superficial area of the vent is 240 mm 2 . 
     If the desired air flow rate exists in the textile  65 , optionally, the holes in a peripheral edge region of a desired vent portion are occluded ( 56 A). The peripheral edge region of the vent portion is overmolded to the mask frame  3310 . Since the holes that existed at the peripheral edge region have been occluded, the airflow rate of the vent portion should not significantly differ after overmolding. 
     In some examples, the airflow rate may be measured ( 58 ) after the vent portion is cut from the textile, and also the vents may be measured ( 61 ) after being overmolded to the mask frame. This enables the airflow rate to be known and determined to be within the desired predetermined range after certain manufacturing steps. This may prevent wastage so that the part may be discarded as soon as it is known that it is not within the desired predetermined range. 
     The porosity of the vent portion can be reduced by several ways, including: heat staking, plastic deformation by compression, ultrasonic welding, applying a sealant (e.g. hot melt adhesive) and applying a thin film. Preferably, heat staking by a staking punch  68  is used to reduce porosity due to increased precision, greater certainty of occlusion of holes in the textile, manufacturing speed, good visual appeal after heat staking, and no additional material is required. Some material shrinkage occurs when heating a plastic material which is accounted for by having excess material surrounding the specific physical dimension for the shape of the vent. The porosity of the vent portion is reduced by partially occluding or by fully occluding holes in the vent portion. The staking punch  68  may use several heat weld heads of various sizes to perform the heat staking. The size of the heat weld head is selected depending on the airflow rate of the vent where a larger size is used if the airflow rate is very high. 
     The order of the cutting and porosity reduction steps may be interchanged. In other words, the porosity reduction may be performed first on the textile  65  and then the vent portion is cut from the textile  65 . In such a scenario, the cutting by the cutter  67  can be eliminated. 
     Any area or region of the vent portion may be selected to reduce porosity. Preferably, the porosity of a substantially continuous peripheral edge region of the vent portion is reduced. This provides good visual appeal because this is adjacent to or at the location where the vent portion is overmolded to the mask frame. Any visual differences between the peripheral edge region and the rest of the vent portion may be less noticeable to the human eye at this location since it may appear to be a defined edge of the mask frame  3310  for receiving the vent  3400 . Alternatively, the area for porosity reduction may be in the form of a character/letter or logo in a central region  79  of the vent  3400  to enhance visual impact and improve brand awareness. It may also be used as a replacement indicator for the patient  1000  to replace the vent  3400  after a certain period of use. 
     After reducing the porosity of a region of the vent portion, the airflow rate of the vent portion is again measured by the airflow meter  66  to confirm that the airflow rate is now within the desired predetermined range of about 47 to 53 liters per minute at 20 cm H 2 O pressure. If the airflow rate is not within the desired predetermined range, then the vent portion may undergo heat staking again or the vent portion is discarded. This minimizes wastage by avoiding having to discard a mask frame with an overmolded defective vent, when only the defective vent portion can be discarded. In a further example for nasal pillows, it also avoids discarding a mask frame which has an air delivery tube overmolded to it. 
       FIGS.  156  and  158    show a section of a textile  65  before heat staking. Loose ends  81  of vertically oriented fibers  80  (warp) along the top edge of the textile  65  are visible. The opening of the voids  83  are defined between the vertically oriented fibers  80  and the horizontally oriented fibers  82  (weft). Some voids  83  are considered more porous than other voids because they have a larger opening and therefore permit greater airflow through it and increased exhaled air washout. 
       FIGS.  157  and  159    show a section of textile  65  after heat staking. The voids  83  that previously existed before heat staking have been occluded to reduce or prevent airflow through it.  FIG.  157    is a graphical depiction for illustrative purposes only, however, a microscope photograph is likely to show that discrete fibers of the textile after heat staking are visually undetectable due to material deformation and melting of the fibers caused by the heat and compression of the heat staking process. The sectional side view depicted in  FIG.  159    illustrates that the discrete fibers of the textile  65  after heat staking are visually undetectable due to material deformation and melting of the fibers caused by the heat and compression of the heat staking process. Therefore this region of the vent portion after heat staking becomes substantially air impermeable, in order to selectively adjust the overall airflow rate of the entire vent portion. 
     Turning to  FIG.  155   , a section of textile  65  has two vent portions  72 ,  73  that have been heat staked intended for left side and right side vents. A notional left side vent portion  84  is also depicted showing the outline of the vent portion prior to heat staking. The vent portions  72 ,  73  are in the shape of a semi-circle or are D-shaped. Each vent portion  72 ,  73  substantially conform to the shape of a vent aperture in the mask frame  3310 . The vent portions  73 ,  73  are initially made slightly larger than the vent aperture to assist with overmolding and also to take into account plastic shrinkage that is expected due heat from the later steps of heat staking and overmolding. Preferably, the peripheral edge of each vent portion  72 ,  73  is continuously curved or arcuate with no straight lines. Two corners  74 ,  75  with an acute angle are the distal ends of a longer side  76  of the vent portion. The longer side  76  has a length of about 19 mm to about 24 mm, preferably, in the range of 21.6 mm to 22 mm. Opposite the longer side  76  is a third corner  77  of the vent portion with an obtuse angle. A substantially continuous peripheral edge region  78  of the vent portion is heat staked to reduce porosity of the textile material  65  in this region. The peripheral edge region  78  may have location alignment features/pins. The width for the peripheral edge region  78  to be heat staked is selected based on the amount of porosity to be reduced in order to obtain the desired air flow rate overall through the vent. A central region  79  located within the peripheral edge region  78  has no heat staking applied to it, and the porosity remains as per the original textile  65 . 
     Sound caused by exhaled air (including exhaled carbon dioxide) passing through the vent  3400  is minimised because of greater air diffusion as it passes through the textile/interlaced fibers, in particular, for nasal pillows when a patient  1000  exhales out of their nose and the exhaled air (including exhaled carbon dioxide) flows out through the vent  3400 . Diffusion of the exhaled air (including exhaled carbon dioxide) avoids direct or focused airflow to a bed partner  1100  or the patient  1000  depending on vent orientation and sleeping position. Referring to  FIGS.  167  to  175   , in one example of the present technology, the vent  3400  is significantly more diffused than the multi-hole vent of a SWIFT FX™ nasal pillows mask by ResMed Limited. Turning to  FIG.  175   , at close distances to the vent at about 100 mm, the air speed of exhaled air (including exhaled carbon dioxide) from the vent  3400  of the present technology is about 5 times less than the SWIFT FX™ nasal pillows mask. In other words, the patient  1000  and their bed partner  1100  are less likely to feel the exhaled air (including exhaled carbon dioxide) from the vent  3400  compared to the multi-hole vent. This improves comfort for the patient  1000  and their bed partner  1100 . The average air velocity has a non-linear curve and was measured using a directional hot wire anemometer in a closed room. Air velocity is a major factor on whether exhaled air (including exhaled carbon dioxide) passing through the vent  3400  may be felt by a person. Other factors which may affect what is felt by a person that were not measured in  FIGS.  167  to  175    include ambient room temperature, people&#39;s hair follicle density and people&#39;s skin sensitivity. At greater distances from the vent, the air speed of exhaled air (including exhaled carbon dioxide) from both vents will approach zero and be indistinguishable from the surrounding ambient conditions. However, the air speed of exhaled air (including exhaled carbon dioxide) from the vent  3400  of the present technology will reach this limit of zero at a closer distance to the vent  3400  than the multi-hole vent. Although a specific multi-hole vent that has been used in the SWIFT FX™ nasal pillows mask was compared, it is envisaged that the vent  3400  of the present technology is superior in terms of noise level and air diffusion compared to most multi-hole vents. 
     Another method for manufacturing a vent  3400  for washout of exhaled air (including exhaled carbon dioxide) from a patient interface  3000  is also provided. A vent portion is cut from a semi-permeable material having a thickness less than 0.45 mm and a predetermined amount of porosity to diffuse airflow. Cutting occurs if the semi-permeable material is provided in the form of a larger sheet, ribbon or roll, particularly with a large width. The vent portion is molecularly adhered to a mask frame  3310  of a patient interface to form the vent  3400 . The predetermined amount of porosity is such that an airflow rate of approximately 47 to 53 liters per minute at 20 cm H 2 O pressure of respiratory gas from the patient interface  3000  is obtained. Also, the predetermined amount of porosity is such that an A-weighted sound power level is less than or equal to 25 dbA, with uncertainty 3 dbA and an A-weighted sound pressure at a distance of 1 meter is less than or equal to 17 dbA with uncertainty 3 dbA are generated. Preferably the A-weighted sound power level dbA (uncertainty) is about 22.1 (3) dbA and the A-weighted sound pressure dbA (uncertainty) is about 14.1 (3) dbA measured using ISO 17510-2:2007, 10 cmH2O pressure at 1 m. In other words, the vent  3400  of the present technology is quieter than the multi-hole vents of prior masks as described in the table of noise of prior masks described under the heading of Description of the Related Art. The patient  1000  and their bed partner  1100  are less likely to hear sound caused by exhaled air (including exhaled carbon dioxide) passing through the vent  3400  compared to a multi-hole vent. Heat staking or other previously described techniques of occluding the holes may also be used to specifically adjust the airflow rate of the vent portion until the desired airflow rate is achieved, if necessary. 
     The vent portion  72  is held in a mold  70  to enable the vent portion  72  to be overmolded to the mask frame  3310  in a molding machine  71 . The semi-permeable material may be textile or non-textile so long as the thickness is less than about 0.45 mm. A thin vent is one feature that enables a compact and unobtrusive patient interface  3000  to be provided. Also, a thin vent molded to the mask frame  3310  has visual appeal because the fusion between these two parts appear seamless and flush and the thin vent does not have to excessively protrude inwardly or outwardly relative to the mask frame  3310 . Also, a thin vent is light weight since less material is required, reducing the overall weight of the patient interface  3000 . For example, the textile material  65  may weigh about 200 to 250 grams per m 2 . The textile material  65  may weigh about 217 to about 234 grams per m 2 . Smaller diameter fibers can produce a thinner textile material to achieve the same air flow rate, and this would produce an more light weight vent  3400 . 
     The vent  3400  of the patient interface  3000  is simple to clean and is re-usable. A mild cleaning solution or soapy water can be used to clean the vent  3400 . Hot water can also be used to flow through the vent  3400  for cleaning. The vent  3400  can be hand washed and rinsed without disassembly from the mask frame  3310  because it is permanently connected, for example, overmolded, to the mask frame  3310 . Less detachable parts for the patient interface  3000  avoids the possibility of losing individual parts and also reduces cleaning time by not having to detach and re-attach many parts from one another. If the vent  3400  is formed by interlaced plastic fibers, durability of the vent  3400  is maintained even after repeated cleaning in contrast to a vent made from another less durable material, for example, a cloth textile or GORE-TEX™. In contrast to the vent  3400  of the present technology, GORE-TEX™ is a non-woven material and its voids occlude very quickly during use from atmospheric particulate matter being trapped in the voids, eventually leading to significant blockage of the vent. Blockage of the vent causes inadequate washout of exhaled air (including exhaled carbon dioxide CO2) by the patient leading to an increase in CO2 levels in the blood and ultimately hypoxia due to CO2 re-breathing. Also, the voids in GORE-TEX™ are invisible to the naked eye meaning that the patient is unable to visually determine blockage caused by mucous, dust, dirt, and grime. Washing the GORE-TEX™ material with water does not alleviate this problem because the purpose of GORE-TEX™ is to repel water. In contrast to the vent  3400  of the present technology, GORE-TEX™ is not a robust material as it is similar to paper and easily tears and subject to damage easily if attempting to clean with a brush or fingers. This is a further reason that GORE-TEX™ cannot be cleaned and re-used because it would be irreparably damaged by the cleaning process due to its paper like fragility. A sintered material such as a sintered cylindrical block for a vent suffers similar deficiencies as with GORE-TEX™ in that the fine pores of the sintered material become clogged after use and cannot be properly cleaned for re-use and visual inspection of blockage is not discernible to the naked eye. Vents made from non-plastic materials are not as easily manufactured as the vent  3400  of the present invention because they may require an additional manufacturing step or cannot be permanently connected to a mask frame using an integral bond such as overmolding. Without an integral bond between the vent and the mask frame there may a reduction in durability and reliability, and/or the visual aesthetics are less pleasing. 
     In one example, the vent  3400  has consistent and continual air flow through the vent  3400  to enable proper washout of exhaled air (including exhaled carbon dioxide). The vent  3400  is fast to manufacture and is fast to assemble thereby leading to low cost production compared to some prior art vent manufacturing methods. This may be attributed to its relatively simple geometric shape, low amount of processing steps to have the vent  3400  permanently attached to the mask frame  3310 , and also a low amount of processing steps and types of equipment needed in the event adjustment to the airflow rate is required. Also, if the vent  3400  is a textile formed by interlaced plastic fibers, it has a fabric look which is aesthetically pleasing for patients  1000  and their bed partners  1100  compared to a multi-hole vent or a sintered block vent. 
     Another example is described for manufacturing the vent  3400 . The plastic fibers are spun monofilaments and are woven or knitted on a narrow weaving loom into an interlaced structure. The interlaced structure may be in the form of narrow ribbons, rather than a roll with a large width. Alternatively, the plastic fibers may be multifilament which may provide tighter turns and more a tortuous path than monofilaments. This permits greater control of the permeability of the textile  65  because heat slitting is avoided. Another advantage is that the heat staking step of the earlier example described for controlling and correcting the air flow rate can be avoided or the number of heat weld heads for the staking punch  68  may be reduced. Therefore, the textile  65  of the vent  3400  may be manufactured within the desired predetermined range and heat staking is used only to blank off a peripheral edge area of the vent  3400  for the purposes of overmolding to the mask frame  3310  for permanent attachment. 
     It may be possible to further limit any unintended variation of the air flow rate of the vent  3400  during manufacture. In the examples described earlier, the roll or ribbon  65  may be calendered which is a finishing process where the roll or ribbon  65  is passed under rollers at high temperatures and pressures to produce a flat sheet. However, in another example, the roll or ribbon  65  may not be non-calendered first but instead is first cut into narrow ribbons having a width substantially similar to the height of the vent  3400 . Each narrow ribbon is calendered to make them flat using a heated roller that has a contact surface with a width substantially similar to the width of the ribbon, to ensure that heat and pressure is applied evenly onto the ribbon. Therefore any unintended variation of the air flow rate of the vent  3400  caused by uneven calendering may be avoided. 
     In another example, the textile  65  may be evenly calendered with a predetermined pressure and predetermined level of heat to achieve an air flow rate within the desired predetermined range. Thus, the earlier described heat staking step for the purposes of adjusting the air flow rate by occluding voids may be avoided. 
     In another example, the textile  65  may omit calendering and void occlusion. The textile  65  may be knit or woven into an interlaced structure into narrow ribbons or strips. The textile  65  is then cut using the cutting/fusing techniques described earlier into the shape of the vent portions  72 ,  73 . The vent portions  72 ,  73  are then permanently connected to the frame  3310  or other component in the pneumatic path of the patient interface  3000 . 
     Although the vent  3400  has been described as being made from interlaced plastic fibers, it is envisaged that materials for the fibers apart than plastic may be used that are biocompatible, and have a similar flexural stiffness to prevent the shape, geometry, profile of the vent  3400  from changing during breathing cycles of the patient  1000 . For example, thin metallic wire or yarn may be used. An additive may be sprayed to stiffen the metallic or yarn scaffold of the vent to provide a flexural stiffness to prevent the shape, geometry, profile of the vent  3400  from changing during breathing cycles of the patient  1000 . The vent  3400  is described as having the form of an interlaced structure which includes woven fibers and knitted fibers. 
     Location of Vent  3400   
     In one form of the present technology, vent  3400  is located on, or formed as part of frame  3310 . Specifically, in the example of the technology depicted in  FIGS.  75  and  76    a pair of vents  3400  may be disposed on either side of an anterior surface of the frame  3310 . In one example, the anterior surface of the mask frame  3310  is curved and therefore the vents  3400  are not facing a direction that is perpendicular to the sagittal plane but are rather facing off the perpendicular axis between the sagittal plane and the coronal plane. Positioning the vents  3400  in this manner in the mask frame  3310  directs the flow of air from the vents  3400  towards the lateral sides rather than straight centre which avoids a direct stream of air to a bed partner  1100  if the patient  1000  is directly facing him or her. An area in front of the centre of the patient interface  3000  has a lower average air velocity from the vents  3400  compared to an area along the vent axis i.e. the area along the direction perpendicular to the superficial anterior surface of the vent  3400 . 
     Although the vent  3400  has been described as being permanently connected to the frame  3310 , it is envisaged that the vent  3400  may be located somewhere else in the pneumatic region of the patient interface  3000 , for example, on or proximal to the seal-forming structure  3100  or on a cuff/adaptor  4190  (see  FIGS.  1   b  and  1   c   ), which would allow the washout of exhaled air (including exhaled carbon dioxide). The vent  3400  may be permanently connected to the other pneumatic components in the pneumatic region of the patient interface  3000 , for example, on an elbow if the patient interface  3000  has an elbow to decouple tube torque. 
     The pore size characterisation of the vent  3400  may be estimated using a Bubble Point test method described in American Society for Testing and Materials Standard (ASTM) Method F316. The Bubble Point test is a sensitive visual technique. The textile material  65  may have a bubble point pressure of about 60 to about 100 psig (per square inch gauge). Preferably, the bubble point pressure of the textile material  65  has a bubble point pressure of about 80 psig. 
     In one example of the present technology, the vent  3400  may be provided as a removable vent cap for a patient interface  3000 . The vent cap has a vent frame to removably engage with a vent orifice. The vent orifice may be located in a mask frame, elbow or cushion member/plenum chamber  3200 . The textile material  65  of the vent  3400  is permanently connected to the vent frame. The vent  3400  having a porous region for washout of exhaled air. The textile  65  in the form of interlaced fibers. A tortuous air path for the exhaled air is defined by spaces between the interlaced fibers. The textile is structured such that the shape, geometry and profile of the vent is substantially unchanged during breathing cycles of the patient  1000  and the porous region maintains a substantially constant rate of washout for the exhaled air. 
     Although the vent  3400  has been described as an interlaced structure, it may be possible for the vent  3400  to have a non-woven structure such as a fiber reinforced polymer in the form of an unsealed and porous plastic matrix. A two layered structure for the vent  3400  is possible by having a non-woven structure as a first layer bonded to a woven structure as a second layer. 
     Connection Port  3600   
     Connection port  3600  allows for connection of the patient interface  3000  to a short tube  4180  of the air circuit  4170 , as shown in  FIG.  166   . In one example of the present technology, the short tube  4180  may be connected directly to the patient interface  3000  by the connection port  3600 . The short tube  4180  may be connected to the frame  3310  at the connection port  3600  by insert molding the frame onto the short tube  4180 . The connection port  3600  may be located on the patient interface  3000  and may provide either a fixed or movable connection to the gas delivery tube  4180 . 
     The connection port  3600  may be part of the frame  3310  such that the frame is molded to include the connection port in one piece. Additionally, the connection port  3600  may be connected to the frame  3310  at a limited portion or portions of its periphery. This may result in open areas between the connection port  3600  and the frame  3310  and these open areas may include the vent(s)  3400  described herein. As shown in  FIGS.  10 ,  15  and  18   , the connection port  3600  may be formed at an angle relative to the frame  3310  to direct the tube from the mask at an angle. Also, the connection port  3600  may be angled in any direction and at any angle relative to the frame  3310 . In the illustrated example, the connection port  3600  is angled downward relative to the frame  3310  to cater for a majority of patients who typically have the tube  4180  directed downwards during treatment. This minimises looping of the tube  4180  and may improve seal and stability of the patient interface  3000  during treatment. It may also be possible to form the connection port  3600  separately from the frame  3310  and connect these components such that the connection port  3600  may rotate relative to the frame  3310  using a swivel connection. In such an example, may improve reduce tube torque of the short tube  4180  disrupting sealing forces, or may improve comfort and seal if the short tube  4180  is configured in a tube-up position up over the patient&#39;s head. 
       FIG.  18    shows the short tube  4180  angled downwardly relative to the patient interface  3000  by virtue of its connection to the connection port  3600  which is formed at a downward angle relative to the frame  3310 . This arrangement may prevent the short tube  4180  from looping out away from the patient at a great distance to avoid entanglement. 
     It should also be understood that the flow of gas into the patient interface  3000  may be more evenly distributed in the example of the technology where no elbow is used to connect the air circuit  4170  to the patient interface  3000 . The sharp bend of an elbow may cause a large density of the flow lines on one side of the elbow. This may induce jetting where the flow is condensed and this may result in a suboptimal flow into the patient interface  3000  and, specifically, the nasal pillows  3130 . It should also be understood that the vent  3400 , described above, may contribute to the reduction in jetting. While the use of elbows in prior masks have been to decouple tube torque by allowing at least relative rotational movement between the air circuit  4170  and the frame  3310 , one form of the present technology has a particularly floppy short tube  4180  that is capable of decoupling tube torque that conventional elbows would be responsible for. 
     Forehead Support 
     In one form of the present technology, patient interface  3000  does not include a forehead support. In one form, the patient interface  3000  provides sufficient stability that a forehead support is not required which leads to less obtrusiveness and opens up the eyes and nasal bone. 
     In one alternative form, the patient interface  3000  includes a forehead support. 
     Anti-Asphyxia 
     In one form of the present technology, patient interface  3000  may include an anti-asphyxia valve (AAV). In further examples of the present technology, when a full-face mask is used an AAV may be included with the decoupling structure  4190  (see  FIG.  1   b   ), the air circuit  4170  (see  FIGS.  1   a  to  1   c   ), or the patient interface  3000 . 
     Ports 
     In one form of the present technology, patient interface  3000  may include one or more supplemental oxygen ports  4185  that allow access to the volume within the plenum chamber  3200 . In one form this allows a clinician to supply supplemental oxygen. In one form this allows for the direct measurement of a property gases within the plenum chamber  3200 , such as the pressure. 
     Decoupling Structure(s)  4190   
     In one form, the patient interface  3000  includes at least one decoupling structure, for example, a rotatable cuff or adapter  4190 , as shown in  FIGS.  1   b  and  1   c   , or a ball and socket. Referring to  FIGS.  1   b  and  1   c   , decoupling of a tube-drag force is provided at least in part by short tube  4180 . In this way, short tube  4180  functions at least in part as a decoupling structure  4190 . 
     Referring to  FIGS.  1   b  and  1   c   , at an end of the short tube  4180  is the rotatable cuff or adapter  4190  to facilitate connection to a third end of an additional gas delivery tube  4178  that may be different in at least one aspect from the short tube  4180 . The rotatable cuff  4190  allows the short tube  4180  and the additional gas delivery tube  4178  to rotate relative to one another at respective ends. The additional gas delivery tube  4178  may incorporate similar features to the short tube  4180 , but may have a larger inner diameter (e.g., 18 mm-22 mm). This additional degree of freedom provided to the tubes may help to reduce tube drag forces by alleviating twisting, and therefore kinking, of the air circuit  4170 . Another end of the additional gas delivery tube  4178  may be connected to a PAP device  4000 . 
     Short Tube  4180   
     In one form of the present technology, a short tube  4180  is connected to frame  3310  at the connection port, as shown in  FIG.  166   , and forms part of the air circuit  4170 . 
     The short tube  4180  is a gas delivery tube in accordance with an aspect of the present technology is constructed and arranged to allow a flow of air or breathable gasses between the PAP device  4000  and the patient interface  3000 . 
     Gas delivery tubes are subject to tube drag forces which represent the force subjected to the tube while in use as it lays on the patient and other surfaces (e.g., a bed, a nightstand, a hospital bed, a table, floor, etc.) during use. Since the short tube  4180  is connected to the patient interface  3000  to provide breathable gas to the patient  1000  these tube drag forces can affect the connection between the patient interface  3000  and the patient  1000 . For example, tension and torsion tube drag forces may cause the patient interface  3000  to displace from the patient&#39;s face, thereby causing leakage of the breathable gas from the patient interface  3000 . Thus, it is desirable to decrease the tube drag forces. This may be accomplished by reducing the weight of the short tube  4180 , improving its flexibility (e.g., by decreasing its bend radius such that the tube  4180  can be curved more tightly), and adding at least one degree of freedom for the short tube  4180 . Also, such a reduction in tube drag forces must be accomplished without significantly reducing the strength of the tube  4180  such that it may resist occluding forces, e.g., when a patient may lay his or her arm on the tube  4180  or when twisted into a kinked position. 
       FIGS.  160  to  162    show three side views of an exemplary short tube  4180  in three different states.  FIG.  160    shows the short tube  4180  in a neutral state or normal condition. In the neutral state, the short tube  4180  is not subject to any external forces, i.e., it is not stretched or compressed. The short tube  4180  may be comprised of a web of material  4172  that is spaced between adjacent coils of a helical coil  4174 . The helical coil  4174  of the short tube  4180  may have a width of WC. The web of material  4172  may span the distance between adjacent coils WF. Further, as shown in  FIG.  160   , the web of material  4172  may be folded such that a vertex or peak of the fold  4182  extends radially outward from between adjacent coils. It should be understood that due to the fold of the web of material  4172 , the width of material comprising the web of material  4172  may be wider than the width between adjacent coils WF. Also, the web of material  4172  may be folded along a predetermined fold line  4186 . 
     Also shown in  FIG.  160   , the distance between adjacent coils WF may be equal, or substantially equal, to the width of the helical coil WC when the short tube  4180  is in the neutral state. In such an arrangement, the maximum bend radius R (shown in  FIG.  163   ) of the tube  4180  is decreased and flexibility is improved. This is because an amount of material greater than in prior art tubes must be used to span the distance between adjacent coils. For one, the distance WF being equal to the width of the coil WC results in a larger amount of material to span the distance, and because it is folded an even greater amount of material must be provided to comprise the web of material  4172 . This principle is described in greater detail in relation to  FIG.  163   . The shape of the fold is important to the overall flexibility of the tube. A larger radius in the folds of the web produces a more flexible tube. A very sharp crease makes the tube less flexible. After multiple thermal disinfection cycles, the folds start to relax and the tube becomes less flexible. When the fold is relaxed, it is observed that the fold diameter is reduced relative to the coil diameter and hence the peaks of the folds are lowered. 
     Additionally, in  FIG.  160    it can be seen that the fold of the web of material  4172  extends not only radially outward from the short tube  4180 , but the fold of the web of material  4172  is centrally located between adjacent coils of the helical coil  4174 . Furthermore,  FIG.  160    also shows how the slope of the web of material  4172  may increase towards the vertex or peak of the fold  4182  from adjacent coils of the helical coil  4174 . In other words, the web of material  4172  is flatter further away from the predetermined fold line  4186  and the web of material  4172  becomes steeper and pointier near the vertex or peak of the fold  4182 . 
     Also in  FIG.  160   , as will be discussed in greater detail below, it can be seen that an outer portion or outer surface  4184  of the helical coil  4174  has a curved profile that is rounded over a wide angle. In other words, the helical coil  4174  may have a profile of a portion of the perimeter of an oval. By providing a rounded outer surface or profile  4184  to the helical coil  4174 , a softer and smoother tactile feel may be provided to the patient  1000 . Additionally, this rounded outer surface  4184  may also decrease the propensity of the short tube  4180  to snag on surfaces while in use, such as bedding, the patient&#39;s clothing, bedroom or hospital furniture, etc. As can been in  FIG.  160   , a coil diameter DC can be seen, which is the diameter of one of the plurality of helical coils measured perpendicularly to the longitudinal axis of the short tube  4180 . 
     Another feature that may be seen in  FIG.  160   , the short tube  4180 , in its neutral state, has the fold of the web of material  4172  rising radially outward from the gas delivery tube such that the vertex or peak of the fold  4182  is at substantially the same height, or the same height, as the outer surface  4184  of the helical coil  4174 . The fold of the web of material  4172  also defines a fold diameter DF between opposite vertices of the fold  4182  measured perpendicularly to the longitudinal axis of the short tube  4180 . Said in another way, when the short tube  4180  is in its neutral state, the diameter of the web of material  4172  spanning respective vertices of its fold  4182  across the longitudinal axis of the gas delivery tube may be equal to the diameter of the helical coil  4174  spanning respective outer surfaces  4184  across the longitudinal axis. It could also be said that if the short tube  4180  is laid out straight in a neutral state, that a single cylinder could be circumscribed flush to the vertex or peak of the fold  4182  and the outer surface  4184  of the helical coil  4174 . Also, it may be said that when the short tube  4180  is in a neutral state that the fold diameter DF is equal to, or substantially equal to, the coil diameter DC. 
     Such an arrangement, in conjunction with the rounded outer profile  4184  of the helical coil  4174 , may provide an improved tactile feel, making for a smoother and softer feel for the patient. Additionally, the short tube&#39;s  4180  decreased propensity to snag may also be enhanced by having the vertex or peak of the fold  4182  and the outer surface  4184  of the helical coil  4174  rise to the same height because there is no single surface that protrudes prominently to snag on external surfaces. 
     In another example of the present technology, the web of material  4172  may be folded multiple times in between adjacent coils of the helical coil  4174 . This may allow for additional flexibility of the short tube  4180  along with further extensibility due to the additional amount of material that is between each adjacent coil. Also, in another example of the present technology there may be certain regions or portions along the length of the short tube  4180  where the web of material  4172  is folded between adjacent coils of the helical coil  4174  and other regions of the gas delivery tube where the web of material is not folded. Such an arrangement may allow for varying degrees of flexibility and extensibility along the length of the gas delivery tube. For example, it may be possible to provide portions of the short tube  4180  with increased or decreased stiffness at locations near the patient interface  3000  and the PAP device  4000 . In one example, portions of the short tube  4180  near the patient interface  3000  and the PAP device  400  may have fewer folds per unit length of tube to increase the stiffness of the tube in these regions so as to ensure that kinking is reduced in these regions. Another reason not to fold a section of web of material  4172  could be for manufacturing reasons. For example, not having a fold on the web  4172  at the distal ends where overmolding of a cuff is to occur. This may reduce the tendency of creating a weak spot in the web  4172  where it joins the cuff as a folded web at these locations can get caught in a weak pinched state. 
       FIG.  161    shows another side view of the exemplary short tube  4180 . In this view, the short tube  4180  is in a compressed or contracted state. In this state, the length of the short tube  4180  will be less than its length when it is in the neutral state shown in  FIG.  160   . For example, the short tube  4180  may be compressed to a length that is up to 50% less than in the neutral state. When the short tube  4180  is compressed to its compressed state the web of material  4172  is compressed such that its fold becomes steeper and the distance between adjacent coils WF of the helical coil  4174  decreases. In the compressed state, the distance between adjacent coils WF may decrease to less than the width of the helical coil WC. Also, the vertex or peak of the fold  4182  of the web of material  4172  may be forced further outward in the radial direction such that the vertex or peak rises above the outer surface  4184  of the helical coil  4174 . In other words the web of material  4172  may become taller. This effect may be controlled by the amount of material between adjacent coils and the angle of the fold and the thickness TW of the web of material  4172 . Moreover, it should also be understood that while the width of the helical coil WC may not decrease during compression of the short tube  4180 , the adjacent coils of the helical coil  4174  may be forced together as is common with other springs. Also in  FIG.  161   , it can be seen that when the short tube  4180  is in the compressed state the angle at the vertex or peak  4182  of the fold of the web of material  4172  (i.e., the angle between each portion of the web of material on either side of the predetermined fold line) is decreased and, again, the web of material may become taller. 
       FIG.  162    shows an additional side view of the short tube  4180  when it is in its extended or elongated state. In this state the short tube  4180  may have a length greater than in the neutral state shown in  FIG.  160   . For example, the short tube  4180  may be extended up to 200% of its length when in the neutral state. Also, in this view it can be seen that the distance between adjacent coils WF of the helical coil  4174  increases and the fold of the web of material  4172  becomes flatter. Also, the distance between adjacent coils WF may increase to greater than the width of the helical coil WC. Further, in  FIG.  162    it can be seen that the vertex or peak of the fold  4182  of the web of material  4172  may be forced radially inward such that the vertex or peak descends to below the height of the outer surface  4184  of the helical coil  4174 . Again, this may be controlled by the amount of material between adjacent coils and the angle of the fold. Moreover, it should also be understood that while the width of the helical coil WC may not increase during extension of the short tube  4180 , the adjacent coils of the helical coil  4174  may be forced apart as is common with other springs. Also in  FIG.  162    it can be seen that when the short tube  4180  is in the extended state, the angle at the vertex or peak of the fold of the web of material (i.e., the angle between each portion of the web of material on either side of the predetermined fold line) is increased and, again, the web of material  4172  may become flatter. 
       FIG.  163    shows an exemplary short tube  4180  curved between two ends. When curved as shown in  FIG.  163   , the web of material  4172  between adjacent coils of the helical coil  4174  may be extended at the outer side of the curved portion  4179  and the web of material at the inner portion of the bend  4176  may be compressed. When curved such as this, the limits of the bend radius R may be better understood. In one example, when draped over a cylinder having a 13 mm diameter, the tube may have a bend radius R of 44 mm under its own weight (i.e., with no additional weight applied). The greater the amount of material that comprises the web of material  4172  the lower the possible bend radius R because, as can be seen in  FIG.  163   , the outer side of the curved portion  4179  can only be extended up to the maximum possible distance between adjacent coils WF. At the outer portion of the bend  4179  the short tube  4180  can only bend and extend, at that outer portion  4179 , up to the width of the web of material  4172  provided between adjacent coils. Thus, if more material is provided for the web of material  4172  between adjacent coils flexibility is improved because the short tube  4180  can be flexed such that the outer portion of the bend  4179  is extended further and the maximum bend radius R is decreased. 
     Also, it can be seen that the distance between adjacent coils WF at the inside of the curved inner portion of the bend  4176  is decreased to the point that adjacent coils of the helical coil  4174  are nearly touching. Therefore, the bend radius R is also limited by the web of material  4172  at the inner portion of the bend  4176 . As can be seen in  FIG.  164   , the web of material  4172  is compressed between adjacent coils of the helical coil  4174  at the inner portion of the bend  4176 . Thus, the thicker the web of material  4172  the greater the maximum bend radius R because the greater the amount of material between adjacent coils, the less they are able to approach one another at the inner portion of the bend  4176 . 
     Therefore, to optimize the bend radius R of the short tube  4180  a sufficient width of the web of material  4172  must be provided to allow the outer portion of the bend  4179  to extend to meet the desired bend radius, but also a sufficient thickness of the web of material must be provided to allow adjacent coils of the helical coil  4174  to come together at the inner portion of the bend  4176  to achieve the desired bend radius. 
       FIG.  164    shows a cross-sectional view of an exemplary short tube  4180  taken as shown in  FIG.  163   . This cross-sectional view of the short tube  4180  shows the gas delivery tube in its neutral state such that the distance between adjacent coils WF is equal to the width of the helical coil WC. The short tube  4180  may also have an internal diameter DI that is about 18 mm. The short tube  4180  may have a pitch P of between 3.2 mm to 4.7 mm, or preferably 4.5 mm to 4.7 mm. This view also shows that the helical coil  4174  may have greater thickness TC than the thickness TW of the web of material  4172 . With the helical coil  4174  being thicker than the web of material  4172 , the helical coil is able to provide structural strength and this gives the short tube  4180  a spring effect. Also in this view, it can be seen that the web of material  4172  may have a substantially uniform and/or continuous thickness. 
       FIG.  164    also shows that at least a portion of the web of material  4172  may be asymmetrical about the predetermined fold line  4186 . For example, the web of material  4172  may include a humped portion  4181  adjacent to the helical coil  4174  on one side of the predetermined fold line  4186  and a slanted portion  4183  may be included on the other side adjacent to the other side of the helical coil. Also, the slope of the web of material  4172  to the vertex or peak  4182  of the fold may be steeper on the side of the slanted portion  4183  than on the side of the humped portion  4181 . Due to the different steepnesses, when the short tube  4180  is in the neutral state, the width WFS between the edge of the helical coil on the side of the slanted portion  4183  and the predetermined fold line  4186  may be less than the width WFF between the edge of the helical coil on the side of the humped portion  4181  and the predetermined fold line. Thus, when extended, the web of material  4172  may be extended such WFS may increase more than WFF because a greater amount of material is comprised in that region. In other words, the short tube  4180  may be extended a certain amount in a first direction (e.g., from the slanted portion  4183  to the humped portion  4181 ) and a different amount in a second direction opposite the first direction (e.g., from the humped portion to the slanted portion). Such an arrangement may be advantageous where the patient interface  3000  is attached to the short tube  4180  at one end and the PAP device  4000  at the other, because the patient  1000  may move while wearing the patient interface  3000 , thus necessitating a greater amount of extensibility in the direction of the patient  1000 . The asymmetric profile of the tube  4180  is typically a result of how the tube  4180  was made. Alternatively though, it may also be possible for the web of material  4172  to have substantially symmetrical profile about the predetermined fold line  4186 . 
     The width of the humped portion WH and the width of the slanted portion WS may be different as can be seen in  FIG.  164   . Thus, the web of material  4172  may be flexed over a greater range toward the adjacent coil across the slanted portion  4183  than across the humped portion  4181 . In other words, due to the larger gap at WS a greater amount of flexibility (i.e., smaller bend radius) may exist in this particular region than at WH, which has a smaller gap. Also, because of the smaller gap at WH this portion may be compressible to a lesser extent than at WS, because the web of material  4172  is already closer to the coil  4174  at WH than at WS. 
     Another feature shown in  FIG.  164    is that the superficial surface area (e.g., the outermost surface area of the short tube  4180 ) may be comprised in a greater proportion by the outer surface  4184  of the helical coil  4174  than the web of material  4172  if the helix coil  4174  generally feels better than the web  4172 , particularly if the folds in the web are very sharp. This may provide a better tactile feel for the patient because, as can be seen in  FIG.  164   , the outer surface  4184  of the helical coil  4174  is rounded and therefore smoother than the vertex or peak of the fold  4182  of the web of material  4172 . 
     Also it can be seen in  FIG.  164    that the web of material  4172  and the helical coil  4174  may be integrally bonded so that the interior surface of the short tube  4180  is smooth and continuous. It should be understood that either adjacent sides of the web of material  4172  may be joined to one another to form the smooth and continuous interior surface or the web of material  4172  may be bonded to adjacent sides of adjacent coils of the helical coil  4174 . By forming the short tube  4180  in this manner, such that the interior surface is smooth and continuous, a smoother flow of breathable gas may be provided through the gas delivery tube. Typically, the folds are formed after the overmolding of the cuffs on both ends of the short tube  4180  to prevent tape pinch. 
     It should also be understood that any suitable combination of materials may comprise the web of material  4172  and the helical coil  4174 . The materials of each respective component  4172 ,  4174  may be the same or they may be different in at least one aspect. In one example of the present technology, the web of material  4172  and the helical coil  4174  may be made from a thermoplastic elastomer (TPE) or thermoplastic polyurethane (TPU). The web  4172  and coil  4174  may both be made from the same plastic material (or different blends of the same plastic material) which is advantageous to produce an integral chemical bond (molecular adhesion) between the web  4172  and the coil  4174 . Material choices are constrained by a number of factors. The mechanical properties of the material for the web  4172  for allowing flexibility are a deciding factor. The ability to withstand thermal disinfection is another important factor. Not being sticky and tacky are other factors. Also, the short tube  4180  must avoid occlusion and withstand hoop stress when an external force is applied on the circumferential surface of the tube  4180  which may occur if a patient&#39;s limb lies on top of the short tube  4180 . This is addressed by providing the short tube  4180  with a minimum internal diameter, and specifying the helix pitch and structural rigidity of the helical coil  4174 . 
     The choice of materials may also affect the spring stiffness (P=kx, where P is load, k is stiffness and x is deflection) of the short tube  4180 . The stiffer the spring k, the smaller the deflection under a constant load. The spring rate is the amount of weight required to deflect a spring (any spring) per measurement unit. For example, materials having different moduli of elasticity and different flexural stiffness may be used for the web of material  4172  and the helical coil  4174 , respectively, to create the desired spring stiffness. Similarly, the spring stiffness may also be chosen by using a material with the same modulus of elasticity for both the web of material  4172  and helical coil  4174 . Also, the pitch of the helical coil  4174 , as discussed in reference to  FIG.  164   , may also affect the spring stiffness of the gas delivery tube  4180 . In one example, the spring stiffness may be about 0.03 N/mm. 
       FIG.  165    shows another view of an exemplary short tube  4180  in a bent or curved state. In this view, similar to  FIG.  163   , the short tube  4180  is curved over a radius R. However, in this view the short tube  4180  can be seen draped over the edge of a flat, elevated surface (e.g., a table) to demonstrate how the tube  4180  might bend when subjected to tension at one end due to gravity. The weight of the portion of the short tube  4180  that hangs over the corner of the table may cause extension of the tube  4180  and bending at a region of the tube  4180  near the edge of the table. This view depicts similar bending characteristics to those shown in  FIG.  163   . Specifically, the web of material  4172  is extended at the outer side of the bent region  4179  and compressed at the inner portion of the bend  4176 , such that WF is greater at the outside of the curve than on the inside. 
       FIG.  166    shows an exemplary short tube  4180  attached directly to a patient interface  3000 . In prior masks, the gas delivery tube is attached to a mask through a swivelling elbow. By redirecting the gas delivery tube with a swivelling elbow at its junction with the patient interface, prior art assemblies seek to reduce tube drag forces. However, the inclusion of a swivelling elbow adds weight and parts which can, in turn, mitigate the reduction of tube drag forces. Thus, in accordance with the present technology, the short tube  4180  may be directly connected to a mask frame  3310 .  FIG.  166    further shows that the short tube  4180  may be angled downwardly from the connection to the mask frame  3310 , which may also contribute to reducing tube drag forces. The downward angle may be facilitated in part by the connection port  3600 . 
     Referring again to  FIGS.  1   b  and  1   c   , a short tube  4180  according to the present technology can be seen connecting a patient interface  3000  at a first end. This connection may be the fixed connection described above in relation to  FIG.  166   . In this example, a cuff is overmolded on the first end of the tube  4180  which is then overmolded to a corresponding connection port  3600  defined in the patient interface  3000 . This example is elbow-less in the sense that there is no elbow between the tube  4180  and the mask frame  3310 . In other examples, it is possible for a swivel elbow to be positioned between the tube  4180  and the mask frame  3310  to enable the swivel elbow and the tube  4180  to freely rotate relative to the mask frame  3310 . It should be understood that the patient interfaces  3000  shown in these views are shown in dashed lines to indicate that a variety of different patient interfaces may be connected to the short tube  4180 . At a second end of the short tube  4180  is a rotatable cuff, swivel cuff or adapter  4190  to facilitate connection to a third end of an additional gas delivery tube  4178  that may be different from the short tube  4180 . The rotatable cuff allows the short tube  4180  and the additional gas delivery tube  4178  to rotate relative to one another at respective ends. The additional gas delivery tube  4178  may incorporate similar features to the short tube  4180 , but may have a larger inner diameter (e.g., 18 mm-22 mm). This additional degree of freedom provided to the tubes  4178 ,  4180  may help to reduce tube drag forces by alleviating twisting, decoupling any tube drag forces experienced, and therefore kinking, of the short tube  4180 . A fourth end of the additional gas delivery tube  4178  may be connected to a PAP device  4000 . A two part swivel that is snapped in is in-mold-assembled into the cuff. Alternatively, a one part swivel snapped on is possible. 
     Referring to  FIGS.  203  to  222   , the tube  4180  of the present technology is compared to prior short tubes which have a helical coil. The comparison indicates that the flexural stiffness or floppiness of the tube  4180  of the present technology is superior because it has a lower gram-force (gf) when the tube  4180  is stretched. The lower end of the tubes is held in a fixed position such that the longitudinal axis of the tubes commences from an angle that is perpendicular to the direction of force being applied to elongate the short tubes. In other words, the lower end of the short tube is held so that it is initially parallel and tangent to a horizontal surface (see  FIGS.  203 ,  208 ,  213 ,  218   ). The upper end of the short tubes is held by an Instron machine directly above the held lower end of the short tube. The Instron machine stretches the short tubes by a distance of 30 mm in a series of steps from 0 to 30 mm, to 60 mm, to 90 mm and to 120 mm, in a vertically upwards direction. The Instron machine also measures the force in Newtons at each distance which may correspond to the spring stiffness of the short tube. A torque gauge and force gauge (Torque Gauge RM No. MTSD05997 and Mecmesin Force Gauge RM No, MFGX05996) are used to measure the grams-force at the fixed lower end of the short tube at each distance the short tube is elongated. Since the tubes having different weights and lengths, at the initial position, the Instron machine, torque gauge and force gauge are zeroed. By zeroing the measurement equipment in this manner, the measurements would be independent of weight and length of each tube. A 1 cm grid is also placed in the background to generally indicate the angle of the short tube at each distance. The comparison shows: 
     
       
         
           
               
            
               
                   
               
               
                 Tube 4180 of Present Technology (FIGS. 203 to 207) 
               
            
           
           
               
               
               
               
            
               
                   
                 Distance 
                 Grams-Force 
                 Newtons Force 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 0 
                 0 
                 0 
               
               
                   
                  30 mm 
                 0 
                 0 
               
               
                   
                  60 mm 
                 40 
                  0.2N 
               
               
                   
                  90 mm 
                 80 
                 0.58N 
               
               
                   
                 120 mm 
                 140 
                  2.2N 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
            
               
                   
               
               
                 ResMed™ Swift FX ™ Nasal Pillows Mask tube (FIGS. 208 to 212) 
               
            
           
           
               
               
               
            
               
                 Distance 
                 Grams-Force 
                 Newtons Force 
               
               
                   
               
            
           
           
               
               
               
            
               
                 0 
                 0 
                 0 
               
               
                  30 mm 
                 40 
                  0.1N 
               
               
                  60 mm 
                 120 
                 0.32N 
               
               
                  90 mm 
                 320 
                  1.1N 
               
               
                 120 mm 
                 580 
                  3.1N 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
            
               
                   
               
               
                 Philips Respironics ™ GoLife ™ Nasal Pillows  
               
               
                 Mask tube (FIGS. 213 to 217) 
               
            
           
           
               
               
               
               
            
               
                   
                 Distance 
                 Grams-Force 
                 Newtons Force 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 0 
                 0 
                 0 
               
               
                   
                  30 mm 
                 60 
                 0.24N 
               
               
                   
                  60 mm 
                 160 
                  0.4N 
               
               
                   
                  90 mm 
                 500 
                 0.71N 
               
               
                   
                 120 mm 
                 2820 
                  6.6N 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
            
               
                   
               
               
                 Philips Respironics ™ Wisp ™ Nasal  
               
               
                 Mask tube (FIGS. 218 to 222) 
               
            
           
           
               
               
               
               
            
               
                   
                 Distance 
                 Grams-Force 
                 Newtons Force 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 0 
                 0 
                 0 
               
               
                   
                  30 mm 
                 20 
                 0.04N 
               
               
                   
                  60 mm 
                 120 
                 0.17N 
               
               
                   
                  90 mm 
                 300 
                 0.73N 
               
               
                   
                 120 mm 
                 480 
                  1.4N 
               
               
                   
                   
               
            
           
         
       
     
     The comparison above shows that the short tube  4180  of the present technology only begins to experience tube torque between 30 mm and 60 mm elongation whereas the prior tubes already experience tube torque by 30 mm elongation. At every distance measured, the prior tubes have a significantly higher grams-force indicating that they are less floppy and have a higher flexural stiffness compared to the tube  4180  of the present technology. Therefore seal disruption as a result of tube torque is less likely to occur with the tube  4180  compared to prior tubes. Also, the floppiness of the tube  4180  enables it to be directly connected to the frame  3310  without requiring a swivel elbow or a ball and socket elbow typically used to address tube torque. This eliminates an additional part which leads to overall weight reduction for the patient interface  3000 . Comfort is improved because the tube  4180  is barely felt by the patient  1000  and it provides a greater freedom of movement for the patient  1000  before any tube drag acts to pull the seal-forming structure  3100  off the patient&#39;s face. 
     As described above, as the short tube  4180  is moved relative to the patient interface  3000 , it may create tube drag forces. The tube drag forces herein may comprise forces and/or moments, however it will understood that the term tube drag forces encompasses forces and/or moments unless stated otherwise. 
     One of the causes of such tube drag forces may be bending of the short tube  4180 . For instance, bending created in the short tube  4180  as the patient  1000  turns their body away from the PAP device  4000  may result in tube drag forces at the patient interface  3000 , potentially disrupting the seal, and/or creating discomfort to the patient. 
     To demonstrate the effect of tube drag forces, a simplified representation of a system comprising a patient interface  3000  and a short tube  4180  may be considered. It may be assumed that in this system, the patient interface is placed on the patient  1000 , and the headgear is de-coupled from the patient interface. In this case, any tube drag forces must be reacted by the patient interface  3000 , wherein any moments for instance may be reacted as a force couple on the patient  1000 , and/or any forces may be reacted by equal and opposite reaction forces on the patient  1000 . 
     The resulting tube drag forces at the patient interface  3000  may be related to the structure of the short tube  4180 . More specifically, as the short tube  4180  is bent, the bending stiffness of the short tube  4180  may affect the tube drag forces created at the patient interface  3000 . 
     Typically, when a cylindrical tubular object of constant cross section is fixed at a fixed end and loaded at a free end (i.e. cantilevered), the resulting force and moment at the fixed end can be described as 
     
       
         
           
             d 
             = 
             
               
                 Pl 
                 3 
               
               
                 3 
                 ⁢ 
                 EI 
               
             
           
         
       
     
     (disregarding gravity) wherein d is the deflection, P is the vertical force, l is the length of the tube, E is the elastic modulus of the material and I is the second moment of area of the cross-section. Here, the resulting reactions at the fixed end would be a vertical force of P in the opposite direction, and a moment of  1 P. 
     Applying this to a system comprising a patient interface  3000  and a short tube  4180 , the reactions at the proximal end would be a vertical force of P, and a moment of  1 P, which may form a part of the tube drag force. The above equation may be rearranged to 
     
       
         
           
             P 
             = 
             
               
                 
                   3 
                   ⁢ 
                   dEI 
                 
                 
                   l 
                   3 
                 
               
               . 
             
           
         
       
     
     It then follows that for a given deflection d (i.e. for a given movement by the patient  1000 ), and tube length l, the tube drag force would be increased as EI is increased, or as EI is decreased, tube drag would be decreased. 
     For a circular tube of constant cross section, I may be calculated using the equation 
     
       
         
           
             I 
             = 
             
               
                 
                   π 
                   ⁡ 
                   ( 
                   
                     
                       d 
                       o 
                       4 
                     
                     - 
                     
                       d 
                       i 
                       4 
                     
                   
                   ) 
                 
                 64 
               
               . 
             
           
         
       
     
     Therefore, as an example, for a given inner diameter (di) of 15 mm, a decrease in the outer diameter (do) from 19 mm to 18 mm would decrease tube drag forces by approximately 32%. Similarly, a decrease in the elastic modulus in the material used would achieve a decrease in tube drag forces, although the relationship may be linear in this case. 
     Therefore, while the short tube  4180  in the present technology may not be a circular tube of constant cross section, the total bending stiffness of the short tube  4180  may be a result of geometric and material properties of various portions of the short tube  4180 , such as the web of material  4172  and the helical coil  4174 . 
     Reducing the bending stiffness of the short tube  4180  may result in weakening the structural integrity of the short tube  4180 . That is, as an example, if the thickness of the web of material  4172  was changed by reducing the outer diameter of the short tube  4180 , the bending stiffness and therefore tube drag forces may be reduced, however this may result in a more fragile construction of the short tube  4180  and lead to occlusion of the short tube  4180  during normal use. 
     Therefore an advantage of the present technology is the combination of the geometry and material of the short tube  4180  working to reduce bending stiffness while maintaining appropriate strength to avoid occlusion and be durable. 
     The tube  4180  is substantially silent without a sticky noise/stiction that may occur from axial compression and elongation of the tube  4180 . One example to reduce or eliminate noise may be applying an additive to prevent the coils of the helical coil  4174  sticking to each other. Prior tubes for patient interfaces have been known to suffer from this type of noise which can be annoying to the patient  1000  and their bed partner  1100  when trying to sleep as it is intermittent noise. The tube  4180  is intended to be light weight to minimise tube drag forces caused by the weight of the tube  4180  under gravity. In one example of the present technology, in the neutral state, the length of the tube  4180  may be about 285 mm to 305 mm including the end cuffs and may weigh about 18.7 grams to 19.1 grams. Thus, the weight of the tube  4180  with the end cuffs may be about 62.6 g/m to 65.6 g/m. There is no air leak between the tube  4180  and the end cuffs that are overmolded to the ends of the tube  4180 . One of the end cuffs may be a swivel cuff  4190  to allow 360° relative rotation between the short tube  4180  and the long tube  4178 , while the other end cuff is a frame cuff that does not swivel. The swivel cuff  4190  may have a bump off which provides an external tactile circumferential edge for an index finger of the patient  1000  to disengage the tube  4180  from a tube adapter  4190  connected to a long tube  4178 . The bump off may tolerate a higher force to enhance durability of the swivel end cuff  4190  and short tube  4180  after repetitive engagement and disengagement from the long tube  4178 . 
     Although a single helical coil  4174  has been described, it is envisaged that more than helical coil may be provided for the tube  4180 . Multiple helical coils for the tube  4180  enable multi-start (double start, triple start, etc), in other words, more than one thread. This may permit each helical coil to be made from a different material or have different dimensions in order to enhance floppiness of the tube  4180  for reducing tube drag forces but also to prevent or resist kinking and occlusion by having a strong structure. 
     Mask System 
     One or more of the mask components may configured and arranged together to decouple tube torque to minimise the likelihood of seal disruption. The short tube  4180  is able to decouple tube torque because of its enhanced floppiness and ability to stretch. If tube torque is greater than what the short tube  4180  can decouple, the positioning and stabilising structure  3300  also decouples tube torque. The rigidiser arms  3302  flex in the sagittal plane to decouple tube torque. Also, the cushioning function of the plenum chamber  3200  and/or seal-forming structure  3100  will decouple some amount of tube torque. Any combination of two or more of these features improves the ability to decouple tube torque. The combination of all of these features further enhances the ability to decouple a larger amount of tube torque. 
     One or more of the mask components may be configured and arranged together to improve comfort for the patient  1000 . The short tube  4180  is light weight and the plenum chamber  3200  and seal-forming structure  3100  are also light weight therefore the headgear tension provided by the positioning and stabilising structure  3300  is not required to be uncomfortably high in order to provide a good seal. Reducing the need for an elbow to connect the short tube  4180  to the frame  3310  also reduces overall weight of the patient interface  3000  which lowers the level of headgear tension required by the positioning and stabilising structure  3300 . Also, the perception by the patient  1000  when a patient interface  3000  is light weight is that it is “barely there” such that it does not feel like you are wearing a patient interface  3000  leading to less anxiety and claustrophobia. The shape and flexibility of the rigidiser arms  3302  provide comfort for the patient  1000  because they sit under the cheek bones and also direct the headgear strap  3301  around the patient&#39;s ears which may be sensitive facial regions for some patients  1000 . The strap  3301  is made from a fabric textile and feels good against the patient&#39;s skin because it does not retain surface heat and condensate from perspiration compared to a plastic headgear strap. Also, the strap  3301  being made from a fabric textile is less dense than a plastic material which leads to weight and bulk reduction. The split region  3326  of the strap  3301  enables the patient  1000  to adjust headgear tension to a level they feel is comfortable for them. Any combination of two or more of these features improves comfort for the patient  1000 . The combination of all of these features greatly enhances comfort for the patient  1000 . 
     One or more of the mask components may be configured and arranged together to improve the chances of an optimal seal with the patient  1000 . This may lead to better therapy compliance and an increase in average daily usage by an additional 36 minutes. An optimal seal may be obtained through a combination of improved decoupling of tube torque and also enhanced comfort for the patient  1000  as described above. 
     One or more of the mask components may be configured and arranged together to improve the visual appeal of the patient interface  3000  leading to better therapy compliance, especially for first time patients  1000 . The patient interface  3000  has a low profile and small footprint on the patient&#39;s face because the frame  3310  is not very wide and is also curved to correspond to facial geometry. Also, the unitary strap  3301  with the split region  3326  and the smooth continuous surface of the curved profile of rigidiser arm  3323  is not obtrusive, does not appear bulky or complex and does not cover a large surface area of the patient&#39;s face. Any combination of two or more of these features improves the visual appeal of the patient interface  3000 . The combination of all of these features greatly enhances the visual appeal of the patient interface  3000 . 
     One or more of the mask components may be configured and arranged together to improve assembly and disassembly of the patient interface  3000 . The patient interface  3000  provides simplicity to the patient  1000  as there are two detachable components from the frame  3310 , which are the seal-forming structure  3100  and strap  3301 . Less detachable components also means that the patient interface  3000  is easy to assembly and disassemble when the patient interface  3000  needs to be cleaned. The frame  3310 , plenum chamber  3200 /seal-forming structure  3100  and strap  3301  may be washed individually and on different schedules, for example, the plenum chamber  3200 /seal-forming structure  3100  may be washed more frequently than the strap  3301 . The shape and structure of the components visually and tactilely suggest to the patient  1000  how to assemble and disassemble the patient interface  3000  in an intuitive manner. For example, the mating relationship between the plenum chamber  3200  and the frame  3310  which generates an audible click sound when engagement is correct is intuitive to a patient  1000 . Also, providing visual and tactile indicators on the frame  3310 , plenum chamber  3200  and the positioning and stabilising structure  3300  adds a further guide for the patient  1000  to avoid incorrect assembly/disassembly or misorientation/misalignment of mask components. Some of these features are especially advantageous for patients  1000  in a darkened environment who may have arthritic hands. For example, the audible click sound may be heard, or the touch and feel of the shapes of the mask components and tactile indicators are also useful in low lighting conditions. Also, by simply stretching the strap  3301  to don or doff the patient interface  300  from the patient&#39;s face avoids complicated engagement/disengagement procedures. Any combination of two or more of these features improves the simplicity of the patient interface  3000 . The combination of all of these features greatly enhances the simplicity of the patient interface  3000 . 
     In one example of the present technology, a frame assembly includes the sub-assemblies of the frame  3310 , short tube  4180 , vent  3400  and rigidiser arms  3302 . The sub-assemblies of the frame assembly are permanently connected to each other, for example, the frame  3310  and short tube  4180  are permanently connected to each other, the frame  3310  and rigidiser arms  3302  are permanently connected to each other, and the frame  3310  and the vent  3400  are permanently connected to each other. A cushion assembly is removably engageable with the frame assembly. The cushion assembly includes the seal-forming structure  3100 , plenum chamber  3200 , retaining structure  3242 , and plenum connection region  3240 . The strap  3301  is removably engageable with the frame assembly, in particular, with the rigidiser arms  3302 . 
     Although a strap  3301  made from fabric has been described, it is envisaged that the strap may be made from silicone or a plastic material at least at a distal end. A silicone strap enables overmolding to the plenum chamber  3200  for a permanent connection. 
     Preventing Incorrect Assembly and Disassembly of Mask System 
     Referring to  FIGS.  187  to  190   , the patient interface  3000  is provided with visual indicators and tactile indicators to prevent or minimise misorientation when engaging mask components together. They also provide intuitiveness to patients  1000  when disengaging mask components from each other. In  FIGS.  187  and  188   , on the outer surface  3355  of the extension  3350  of the rigidiser arms  3302  there is pad printing  3290  provided. The mask name and brand logo are pad printed indicate orientation to the patient  1000  where the words are oriented the right side up. These provide a visual indication for the patient  1000 . In  FIG.  189   , there is raised/embossed text  3291  near an upper edge the frame  3310 . This provides the patient  1000  with a visual and tactile indicator of the whether the frame  3310  is oriented up or down, and especially useful in low light conditions when attaching the strap  3301  to the rigidiser arm  3302 . Also, there is recessed text  3292  on the outer surface of the rigidiser arm  3302 . This provides the patient  1000  with a visual and tactile indicator of the orientation of the rigidiser arm  3302  and is helpful when attaching the strap  3301  to the rigidiser arm  3302 . There may be pad printing  3293  on one side of the plenum chamber  3200 . The pad printing  3293  may indicate the Left pillow  3130  and Right pillow  3130  and also the size of the seal-forming structure  3100  (Small, Medium, Large). For example, when the patient  1000  sees the pad printing  3293  on the plenum chamber  3200 , they would be aware that they are facing the top surface of the plenum chamber  3200 . All these visual and tactile indicators assist the patient  1000  in identifying the sides and surfaces of the patient interface  3000  to avoid misorientation and improper assembly and disassembly. This may avoid inadvertent damage to the patient interface  3000  and also ease any user frustration associated with assembly and disassembly. 
     PAP Device  4000   
     A PAP device  4000  in accordance with one aspect of the present technology comprises mechanical and pneumatic components  4100 , electrical components  4200  and is programmed to execute one or more algorithms  4300 . The PAP device may have an external housing  4010 , formed in two parts, an upper portion  4012  of the external housing  4010 , and a lower portion  4014  of the external housing  4010 . In alternative forms, the external housing  4010  may include one or more panel(s)  4015 . The PAP device  4000  may comprise a chassis  4016  that supports one or more internal components of the PAP device  4000 . In one form a pneumatic block  4020  is supported by, or formed as part of the chassis  4016 . The PAP device  4000  may include a handle  4018 . 
     The pneumatic path of the PAP device  4000  may comprise an inlet air filter  4112 , an inlet muffler, a controllable pressure device capable of supplying air at positive pressure (e.g., a controllable blower  4142 ), and an outlet muffler. One or more pressure sensors and flow sensors may be included in the pneumatic path. 
     The pneumatic block  4020  may comprise a portion of the pneumatic path that is located within the external housing  4010 . 
     The PAP device  4000  may have an electrical power supply  4210  and one or more input devices  4220 . Electrical components  4200  may be mounted on a single Printed Circuit Board Assembly (PCBA)  4202 . In an alternative form, the PAP device  4000  may include more than one PCBA  4202 . 
     PAP Device Mechanical &amp; Pneumatic Components  4100   
     Air Filter(s)  4110   
     A PAP device  4000  in accordance with one form of the present technology may include an air filter  4110 , or a plurality of air filters  4110 . 
     In one form, an inlet air filter  4112  is located at the beginning of the pneumatic path upstream of a controllable blower  4142 . See  FIG.  3     c.    
     In one form, an outlet air filter  4114 , for example an antibacterial filter, is located between an outlet of the pneumatic block  4020  and a patient interface  3000 . See  FIG.  3     c.    
     Pressure Device  4140   
     In a form of the present technology, a pressure device for producing a flow of air at positive pressure is a controllable blower  4142 . For example the blower  4142  may include a brushless DC motor with one or more impellers housed in a volute. The blower  4142  may be capable of delivering a supply of air, for example about 120 litres/minute, at a positive pressure in a range from about 4 cmH2O to about 20 cmH2O, or in other forms up to about 30 cmH2O. 
     Humidifier  5000   
     Humidifier Overview 
     In one form of the present technology there is provided a humidifier  5000 , as shown in  FIG.  3   b   , that may comprise a water reservoir and a heating plate. 
     Glossary 
     For the purposes of the present technology disclosure, in certain forms of the present technology, one or more of the following definitions may apply. In other forms of the present technology, alternative definitions may apply. 
     General 
     Air: In certain forms of the present technology, air supplied to a patient may be atmospheric air, and in other forms of the present technology atmospheric air may be supplemented with oxygen. 
     Continuous Positive Airway Pressure (CPAP): CPAP treatment will be taken to mean the application of a supply of air or breathable gas to the entrance to the airways at a pressure that is continuously positive with respect to atmosphere, and preferably approximately constant through a respiratory cycle of a patient. In some forms, the pressure at the entrance to the airways will vary by a few centimeters of water within a single respiratory cycle, for example being higher during inhalation and lower during exhalation. In some forms, the pressure at the entrance to the airways will be slightly higher during exhalation, and slightly lower during inhalation. In some forms, the pressure will vary between different respiratory cycles of the patient, for example being increased in response to detection of indications of partial upper airway obstruction, and decreased in the absence of indications of partial upper airway obstruction. 
     Aspects of PAP Devices 
     Air circuit: A conduit or tube constructed and arranged in use to deliver a supply of air or breathable gas between a PAP device and a patient interface. In particular, the air circuit may be in fluid connection with the outlet of the pneumatic block and the patient interface. The air circuit may be referred to as air delivery tube. In some cases there may be separate limbs of the circuit for inhalation and exhalation. In other cases a single limb is used. 
     APAP: Automatic Positive Airway Pressure. Positive airway pressure that is continually adjustable between minimum and maximum limits, depending on the presence or absence of indications of SDB events. 
     Blower or flow generator: A device that delivers a flow of air at a pressure above ambient pressure. 
     Controller: A device, or portion of a device that adjusts an output based on an input. For example one form of controller has a variable that is under control the control variable that constitutes the input to the device. The output of the device is a function of the current value of the control variable, and a set point for the variable. A servo-ventilator may include a controller that has ventilation as an input, a target ventilation as the set point, and level of pressure support as an output. Other forms of input may be one or more of oxygen saturation (SaO2), partial pressure of carbon dioxide (PCO2), movement, a signal from a photoplethysmogram, and peak flow. The set point of the controller may be one or more of fixed, variable or learned. For example, the set point in a ventilator may be a long term average of the measured ventilation of a patient. Another ventilator may have a ventilation set point that changes with time. A pressure controller may be configured to control a blower or pump to deliver air at a particular pressure. 
     Therapy: Therapy in the present context may be one or more of positive pressure therapy, oxygen therapy, carbon dioxide therapy, control of dead space, and the administration of a drug. 
     Motor: A device for converting electrical energy into rotary movement of a member. In the present context the rotating member is an impeller, which rotates in place around a fixed axis so as to impart a pressure increase to air moving along the axis of rotation. 
     Positive Airway Pressure (PAP) device: A device for providing a supply of air at positive pressure to the airways. 
     Transducers: A device for converting one form of energy or signal into another. A transducer may be a sensor or detector for converting mechanical energy (such as movement) into an electrical signal. Examples of transducers include pressure sensors, flow sensors, carbon dioxide (CO2) sensors, oxygen (O2) sensors, effort sensors, movement sensors, noise sensors, a plethysmograph, and cameras. 
     Aspects of the Respiratory Cycle 
     Apnea: Preferably, apnea will be said to have occurred when flow falls below a predetermined threshold for a duration, e.g. 10 seconds. An obstructive apnea will be said to have occurred when, despite patient effort, some obstruction of the airway does not allow air to flow. A central apnea will be said to have occurred when an apnea is detected that is due to a reduction in breathing effort, or the absence of breathing effort. 
     Duty cycle: The ratio of inhalation time, Ti to total breath time, Ttot. 
     Effort (breathing): Preferably breathing effort will be said to be the work done by a spontaneously breathing person attempting to breathe. 
     Expiratory portion of a breathing cycle: The period from the start of expiratory flow to the start of inspiratory flow. 
     Flow limitation: Preferably, flow limitation will be taken to be the state of affairs in a patient&#39;s respiration where an increase in effort by the patient does not give rise to a corresponding increase in flow. Where flow limitation occurs during an inspiratory portion of the breathing cycle it may be described as inspiratory flow limitation. Where flow limitation occurs during an expiratory portion of the breathing cycle it may be described as expiratory flow limitation. 
     Hypopnea: Preferably, a hypopnea will be taken to be a reduction in flow, but not a cessation of flow. In one form, a hypopnea may be said to have occurred when there is a reduction in flow below a threshold for a duration. In one form in adults, the following either of the following may be regarded as being hypopneas: 
     (i) a 30% reduction in patient breathing for at least 10 seconds plus an associated 4% desaturation; or 
     (ii) a reduction in patient breathing (but less than 50%) for at least 10 seconds, with an associated desaturation of at least 3% or an arousal. 
     Inspiratory portion of a breathing cycle: Preferably the period from the start of inspiratory flow to the start of expiratory flow will be taken to be the inspiratory portion of a breathing cycle. 
     Patency (airway): The degree of the airway being open, or the extent to which the airway is open. A patent airway is open. Airway patency may be quantified, for example with a value of one (1) being patent, and a value of zero (0), being closed. 
     Positive End-Expiratory Pressure (PEEP): The pressure above atmosphere in the lungs that exists at the end of expiration. 
     Peakflow (Qpeak): The maximum value of flow during the inspiratory portion of the respiratory flow waveform. 
     Respiratory flow, airflow, patient airflow, respiratory airflow (Qr): These synonymous terms may be understood to refer to the PAP device&#39;s estimate of respiratory airflow, as opposed to “true respiratory flow” or “true respiratory airflow”, which is the actual respiratory flow experienced by the patient, usually expressed in litres per minute. 
     Tidal volume (Vt): The volume of air inhaled or exhaled during normal breathing, when extra effort is not applied. 
     (inhalation) Time (Ti): The duration of the inspiratory portion of the respiratory flow waveform. 
     (exhalation) Time (Te): The duration of the expiratory portion of the respiratory flow waveform. 
     (total) Time (Ttot): The total duration between the start of the inspiratory portion of one respiratory flow waveform and the start of the inspiratory portion of the following respiratory flow waveform. 
     Typical recent ventilation: The value of ventilation around which recent values over some predetermined timescale tend to cluster, that is, a measure of the central tendency of the recent values of ventilation. 
     Upper airway obstruction (UAO): includes both partial and total upper airway obstruction. This may be associated with a state of flow limitation, in which the level of flow increases only slightly or may even decrease as the pressure difference across the upper airway increases (Starling resistor behaviour). 
     Ventilation (Vent): A measure of the total amount of gas being exchanged by the patient&#39;s respiratory system, including both inspiratory and expiratory flow, per unit time. When expressed as a volume per minute, this quantity is often referred to as “minute ventilation”. Minute ventilation is sometimes given simply as a volume, understood to be the volume per minute. 
     PAP Device Parameters 
     Flow rate: The instantaneous volume (or mass) of air delivered per unit time. While flow rate and ventilation have the same dimensions of volume or mass per unit time, flow rate is measured over a much shorter period of time. Flow may be nominally positive for the inspiratory portion of a breathing cycle of a patient, and hence negative for the expiratory portion of the breathing cycle of a patient. In some cases, a reference to flow rate will be a reference to a scalar quantity, namely a quantity having magnitude only. In other cases, a reference to flow rate will be a reference to a vector quantity, namely a quantity having both magnitude and direction. Flow will be given the symbol Q. Total flow, Qt, is the flow of air leaving the PAP device. Vent flow, Qv, is the flow of air leaving a vent to allow washout of exhaled gases. Leak flow, Ql, is the flow rate of unintentional leak from a patient interface system. Respiratory flow, Qr, is the flow of air that is received into the patient&#39;s respiratory system. 
     Leak: Preferably, the word leak will be taken to be a flow of air to the ambient. Leak may be intentional, for example to allow for the washout of exhaled CO 2 . Leak may be unintentional, for example, as the result of an incomplete seal between a mask and a patient&#39;s face. 
     Pressure: Force per unit area. Pressure may be measured in a range of units, including cmH2O, g-f/cm 2 , hectopascal. 1 cmH2O is equal to 1 g-f/cm 2  and is approximately 0.98 hectopascal. In this specification, unless otherwise stated, pressure is given in units of cmH 2 O. For nasal CPAP treatment of OSA, a reference to treatment pressure is a reference to a pressure in the range of about 4-20 cmH 2 O, or about 4-30 cmH 2 O. The pressure in the patient interface is given the symbol Pm. 
     Sound Power: The energy per unit time carried by a sound wave. The sound power is proportional to the square of sound pressure multiplied by the area of the wavefront. Sound power is usually given in decibels SWL, that is, decibels relative to a reference power, normally taken as 10 −12  watt. 
     Sound Pressure: The local deviation from ambient pressure at a given time instant as a result of a sound wave travelling through a medium. Sound power is usually given in decibels SPL, that is, decibels relative to a reference power, normally taken as 20×10 −6  pascal (Pa), considered the threshold of human hearing. 
     Anatomy of the Face 
     Ala: the external outer wall or “wing” of each nostril (plural: alar) 
     Alare: The most lateral point on the nasal ala. 
     Alar curvature (or alar crest) point: The most posterior point in the curved base line of each ala, found in the crease formed by the union of the ala with the cheek. 
     Auricula or Pinna: The whole external visible part of the ear. 
     (nose) Bony framework: The bony framework of the nose comprises the nasal bones, the frontal process of the maxillae and the nasal part of the frontal bone. 
     (nose) Cartilaginous framework: The cartilaginous framework of the nose comprises the septal, lateral, major and minor cartilages. 
     Columella: the strip of skin that separates the nares and which runs from the pronasale to the upper lip. 
     Columella angle: The angle between the line drawn through the midpoint of the nostril aperture and a line drawn perpendicular to the Frankfurt horizontal while intersecting subnasale. 
     Frankfort horizontal plane: A line extending from the most inferior point of the orbital margin to the left tragion. The tragion is the deepest point in the notch superior to the tragus of the auricle. 
     Glabella: Located on the soft tissue, the most prominent point in the midsagittal plane of the forehead. 
     Lateral nasal cartilage: A generally triangular plate of cartilage. Its superior margin is attached to the nasal bone and frontal process of the maxilla, and its inferior margin is connected to the greater alar cartilage. 
     Greater alar cartilage: A plate of cartilage lying below the lateral nasal cartilage. It is curved around the anterior part of the naris. Its posterior end is connected to the frontal process of the maxilla by a tough fibrous membrane containing three or four minor cartilages of the ala. 
     Nares (Nostrils): Approximately ellipsoidal apertures forming the entrance to the nasal cavity. The singular form of nares is naris (nostril). The nares are separated by the nasal septum. 
     Naso-labial sulcus or Naso-labial fold: The skin fold or groove that runs from each side of the nose to the corners of the mouth, separating the cheeks from the upper lip. 
     Naso-labial angle: The angle between the columella and the upper lip, while intersecting subnasale. 
     Otobasion inferior: The lowest point of attachment of the auricle to the skin of the face. 
     Otobasion superior: The highest point of attachment of the auricle to the skin of the face. 
     Pronasale: the most protruded point or tip of the nose, which can be identified in lateral view of the rest of the portion of the head. 
     Philtrum: the midline groove that runs from lower border of the nasal septum to the top of the lip in the upper lip region. 
     Pogonion: Located on the soft tissue, the most anterior midpoint of the chin. 
     Ridge (nasal): The nasal ridge is the midline prominence of the nose, extending from the Sellion to the Pronasale. 
     Sagittal plane: A vertical plane that passes from anterior (front) to posterior (rear) dividing the body into right and left halves. 
     Sellion: Located on the soft tissue, the most concave point overlying the area of the frontonasal suture. 
     Septal cartilage (nasal): The nasal septal cartilage forms part of the septum and divides the front part of the nasal cavity. 
     Subalare: The point at the lower margin of the alar base, where the alar base joins with the skin of the superior (upper) lip. 
     Subnasal point: Located on the soft tissue, the point at which the columella merges with the upper lip in the midsagittal plane. 
     Supramentale: The point of greatest concavity in the midline of the lower lip between labrale inferius and soft tissue pogonion 
     Anatomy of the Skull 
     Frontal bone: The frontal bone includes a large vertical portion, the squama frontalis, corresponding to the region known as the forehead. 
     Mandible: The mandible forms the lower jaw. The mental protuberance is the bony protuberance of the jaw that forms the chin. 
     Maxilla: The maxilla forms the upper jaw and is located above the mandible and below the orbits. The frontal process of the maxilla projects upwards by the side of the nose, and forms part of its lateral boundary. 
     Nasal bones: The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, the “bridge” of the nose. 
     Nasion: The intersection of the frontal bone and the two nasal bones, a depressed area directly between the eyes and superior to the bridge of the nose. 
     Occipital bone: The occipital bone is situated at the back and lower part of the cranium. It includes an oval aperture, the foramen magnum, through which the cranial cavity communicates with the vertebral canal. The curved plate behind the foramen magnum is the squama occipitalis. 
     Orbit: The bony cavity in the skull to contain the eyeball. 
     Parietal bones: The parietal bones are the bones that, when joined together, form the roof and sides of the cranium. 
     Temporal bones: The temporal bones are situated on the bases and sides of the skull, and support that part of the face known as the temple. 
     Zygomatic bones: The face includes two zygomatic bones, located in the upper and lateral parts of the face and forming the prominence of the cheek. 
     Anatomy of the Respiratory System 
     Diaphragm: A sheet of muscle that extends across the bottom of the rib cage. The diaphragm separates the thoracic cavity, containing the heart, lungs and ribs, from the abdominal cavity. As the diaphragm contracts the volume of the thoracic cavity increases and air is drawn into the lungs. 
     Larynx: The larynx, or voice box houses the vocal folds and connects the inferior part of the pharynx (hypopharynx) with the trachea. 
     Lungs: The organs of respiration in humans. The conducting zone of the lungs contains the trachea, the bronchi, the bronchioles, and the terminal bronchioles. The respiratory zone contains the respiratory bronchioles, the alveolar ducts, and the alveoli. 
     Nasal cavity: The nasal cavity (or nasal fossa) is a large air filled space above and behind the nose in the middle of the face. The nasal cavity is divided in two by a vertical fin called the nasal septum. On the sides of the nasal cavity are three horizontal outgrowths called nasal conchae (singular “concha”) or turbinates. To the front of the nasal cavity is the nose, while the back blends, via the choanae, into the nasopharynx. 
     Pharynx: The part of the throat situated immediately inferior to (below) the nasal cavity, and superior to the oesophagus and larynx. The pharynx is conventionally divided into three sections: the nasopharynx (epipharynx) (the nasal part of the pharynx), the oropharynx (mesopharynx) (the oral part of the pharynx), and the laryngopharynx (hypopharynx). 
     Materials 
     Silicone or Silicone Elastomer: A synthetic rubber. In this specification, a reference to silicone is a reference to liquid silicone rubber (LSR) or a compression moulded silicone rubber (CMSR). One form of commercially available LSR is SILASTIC (included in the range of products sold under this trademark), manufactured by Dow Corning. Another manufacturer of LSR is Wacker. Unless otherwise specified to the contrary, a preferred form of LSR has a Shore A (or Type A) indentation hardness in the range of about 35 to about 45 as measured using ASTM D2240 
     Polycarbonate: a typically transparent thermoplastic polymer of Bisphenol-A Carbonate. 
     Aspects of a Patient Interface 
     Anti-asphyxia valve (AAV): The component or sub-assembly of a mask system that, by opening to atmosphere in a failsafe manner, reduces the risk of excessive CO 2  rebreathing by a patient. 
     Elbow: A conduit that directs an axis of flow of air to change direction through an angle. In one form, the angle may be approximately 90 degrees. In another form, the angle may be less than 90 degrees. The conduit may have an approximately circular cross-section. In another form the conduit may have an oval or rectangular cross-section. 
     Frame: Frame will be taken to mean a mask structure that bears the load of tension between two or more points of connection with a positioning and stabilising structure. A mask frame may be a non-airtight load bearing structure in the mask. However, some forms of mask frame may also be air-tight. 
     Positioning and stabilising structure: Positioning and stabilising structure will be taken to mean a form of positioning and stabilizing structure designed for use on a head. Preferably the positioning and stabilising structure comprises a collection of one or more struts, ties and stiffeners configured to locate and retain a patient interface in position on a patient&#39;s face for delivery of respiratory therapy. Some ties are formed of a soft, flexible, elastic material such as a laminated composite of foam and fabric. 
     Membrane: Membrane will be taken to mean a typically thin element that has, preferably, substantially no resistance to bending, but has resistance to being stretched. 
     Plenum chamber: a mask plenum chamber will be taken to a mean portion of a patient interface having walls enclosing a volume of space, the volume having air therein pressurised above atmospheric pressure in use. A shell may form part of the walls of a mask plenum chamber. In one form, a region of the patient&#39;s face forms one of the walls of the plenum chamber. 
     Seal: The noun form (“a seal”) will be taken to mean a structure or barrier that intentionally resists the flow of air through the interface of two surfaces. The verb form (“to seal”) will be taken to mean to resist a flow of air. 
     Shell: A shell will preferably be taken to mean a curved structure having bending, tensile and compressive stiffness, for example, a portion of a mask that forms a curved structural wall of the mask. Preferably, compared to its overall dimensions it is relatively thin. In some forms, a shell may be faceted. Preferably such walls are airtight, although in some forms they may not be airtight. 
     Stiffener: A stiffener will be taken to mean a structural component designed to increase the bending resistance of another component in at least one direction. 
     Strut: A strut will be taken to be a structural component designed to increase the compression resistance of another component in at least one direction. 
     Swivel: (noun) A subassembly of components configured to rotate about a common axis, preferably independently, preferably under low torque. In one form, the swivel may be constructed to rotate through an angle of at least 360 degrees. In another form, the swivel may be constructed to rotate through an angle less than 360 degrees. When used in the context of an air delivery conduit, the sub-assembly of components preferably comprises a matched pair of cylindrical conduits. Preferably there is little or no leak flow of air from the swivel in use. 
     Tie: A tie will be taken to be a structural component designed to resist tension. 
     Vent: (noun) the structure that allows a deliberate controlled rate leak of air from an interior of the mask, or conduit to ambient air, to allow washout of exhaled carbon dioxide (CO 2 ) and supply of oxygen (O 2 ). 
     Terms Used in Relation to Patient Interface 
     Curvature (of a surface): A region of a surface having a saddle shape, which curves up in one direction and curves down in a different direction, will be said to have a negative curvature. A region of a surface having a dome shape, which curves the same way in two principle directions, will be said to have a positive curvature. A flat surface will be taken to have zero curvature. 
     Floppy: A quality of a material, structure or composite that is the combination of features of:
         Readily conforming to finger pressure.   Unable to retain its shape when caused to support its own weight.   Not rigid.   Able to be stretched or bent elastically with little effort.       

     The quality of being floppy may have an associated direction, hence a particular material, structure or composite may be floppy in a first direction, but stiff or rigid in a second direction, for example a second direction that is orthogonal to the first direction. 
     Resilient: Able to deform substantially elastically, and to release substantially all of the energy upon unloading, within a relatively short period of time such as 1 second. 
     Rigid: Not readily deforming to finger pressure, and/or the tensions or loads typically encountered when setting up and maintaining a patient interface in sealing relationship with an entrance to a patient&#39;s airways. 
     Semi-rigid: means being sufficiently rigid to not substantially distort under the effects of mechanical forces typically applied during positive airway pressure therapy. 
     OTHER REMARKS 
     A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 
     Unless the context clearly dictates otherwise and where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit, between the upper and lower limit of that range, and any other stated or intervening value in that stated range is encompassed within the technology. The upper and lower limits of these intervening ranges, which may be independently included in the intervening ranges, are also encompassed within the technology, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the technology. Furthermore, where a value or values are stated herein as being implemented as part of the technology, it is understood that such values may be approximated, unless otherwise stated, and such values may be utilized to any suitable significant digit to the extent that a practical technical implementation may permit or require it. It should be further understood that any and all stated values may be variable by up 10-20% from the value stated. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this technology belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present technology, a limited number of the exemplary methods and materials are described herein. 
     When a particular material is identified as being preferably used to construct a component, obvious alternative materials with similar properties may be used as a substitute. Furthermore, unless specified to the contrary, any and all components herein described are understood to be capable of being manufactured and, as such, may be manufactured together or separately. 
     It must be noted that as used herein and in the appended claims, the singular forms “a” “an”, and “the” include their plural equivalents, unless the context clearly dictates otherwise. 
     All publications mentioned herein are incorporated by reference to disclose and describe the methods and/or materials which are the subject of those publications. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present technology is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates, which may need to be independently confirmed. 
     Moreover, in interpreting the disclosure, all terms should be interpreted in the broadest reasonable manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. 
     The subject headings used in the detailed description are included only for the ease of reference of the reader and should not be used to limit the subject matter found throughout the disclosure or the claims. The subject headings should not be used in construing the scope of the claims or the claim limitations. 
     Although the technology herein has been described with reference to particular examples, it is to be understood that these examples are merely illustrative of the principles and applications of the technology. In some instances, the terminology and symbols may imply specific details that are not required to practice the technology. For example, although the terms “first” and “second” may be used, unless otherwise specified, they are not intended to indicate any order but may be utilised to distinguish between distinct elements. Furthermore, although process steps in the methodologies may be described or illustrated in an order, such an ordering is not required. Those skilled in the art will recognize that such ordering may be modified and/or aspects thereof may be conducted concurrently or even synchronously. 
     It is therefore to be understood that numerous modifications may be made to the illustrative examples and that other arrangements may be devised without departing from the spirit and scope of the technology. 
     REFERENCE SIGNS LIST 
       
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 weft knit fabric 
                  64 
               
               
                   
                 textile 
                  65 
               
               
                   
                 airflow meter 
                  66 
               
               
                   
                 cutting tool 
                  67 
               
               
                   
                 staking punch 
                  68 
               
               
                   
                 laser cutter 
                  69 
               
               
                   
                 mold 
                  70 
               
               
                   
                 molding machine 
                  71 
               
               
                   
                 vent portion 
                  72 
               
               
                   
                 vent portion 
                  73 
               
               
                   
                 acute comer of vent portion 
                  74 
               
               
                   
                 acute comer of vent portion 
                  75 
               
               
                   
                 longer side of vent portion 
                  76 
               
               
                   
                 obtuse corner of vent portion 
                  77 
               
               
                   
                 peripheral edge region of vent portion 
                  78 
               
               
                   
                 central region of vent portion 
                  79 
               
               
                   
                 vertically oriented fibers 
                  80 
               
               
                   
                 loose ends 
                  81 
               
               
                   
                 horizontally oriented fibers 
                  82 
               
               
                   
                 voids 
                  83 
               
               
                   
                 notional left side vent portion 
                  84 
               
               
                   
                 course 
                  85 
               
               
                   
                 basic closed loop warp knit 
                  90 
               
               
                   
                 weft knit 
                  100 
               
               
                   
                 rear portion 
                  210 
               
               
                   
                 straps 
                  220 
               
               
                   
                 patient 
                 1000 
               
               
                   
                 bed partner 
                 1100 
               
               
                   
                 top portion of knitted strap 
                 1102 
               
               
                   
                 rear portion of knitted strap 
                 1104 
               
               
                   
                 knitted strap 
                 1105 
               
               
                   
                 lower portion of knitted strap 
                 1106 
               
               
                   
                 connector 
                 1120 
               
               
                   
                 course 
                 1150 
               
               
                   
                 strap 
                 1200 
               
               
                   
                 course 
                 1250 
               
               
                   
                 connected links 
                 2802 
               
               
                   
                 flexible 3D printed textile 
                 2804 
               
               
                   
                 positioning and stabilising  
                 2900 
               
               
                   
                 structure piece 
                   
               
               
                   
                 textile 
                 2904 
               
               
                   
                 hole 
                 2912(1) 
               
               
                   
                 female clips 
                 2912 
               
               
                   
                 female clips 
                 2914 
               
               
                   
                 hole 
                 2914(1) 
               
               
                   
                 holes of rigidiser arm 
                 2922 
               
               
                   
                 3D printed strap 
                 2924 
               
               
                   
                 patient interface 
                 3000 
               
               
                   
                 seal-forming structure 
                 3100 
               
               
                   
                 gas chamber 
                 3104 
               
               
                   
                 distal major side 
                 3104.1 
               
               
                   
                 minor side 
                 3104.2 
               
               
                   
                 proximal major side 
                 3104.3 
               
               
                   
                 nasal flange 
                 3101 
               
               
                   
                 sealing flange 
                 3110 
               
               
                   
                 region 
                 3112.1 
               
               
                   
                 region 
                 3112.2 
               
               
                   
                 region 
                 3112.3 
               
               
                   
                 region 
                 3113 
               
               
                   
                 protruding end 
                 3114 
               
               
                   
                 region 
                 3115 
               
               
                   
                 recessed portion 
                 3116 
               
               
                   
                 region 
                 3117 
               
               
                   
                 peak 
                 3118 
               
               
                   
                 support flange 
                 3120 
               
               
                   
                 compliant region 
                 3122 
               
               
                   
                 nasal pillows 
                 3130 
               
               
                   
                 most posterior portion 
                 3130.1 
               
               
                   
                 frusto-cone 
                 3140 
               
               
                   
                 upper flexible region 
                 3142 
               
               
                   
                 stalk 
                 3150 
               
               
                   
                 flexible region 
                 3152 
               
               
                   
                 plenum chamber 
                 3200 
               
               
                   
                 connection portion 
                 3202 
               
               
                   
                 thickened section 
                 3204 
               
               
                   
                 overhang 
                 3206 
               
               
                   
                 protruding end support section 
                 3208 
               
               
                   
                 anterior wall 
                 3210 
               
               
                   
                 tongue portion 
                 3211 
               
               
                   
                 channel portion 
                 3211.1 
               
               
                   
                 concave lower portion 
                 3212 
               
               
                   
                 posterior wall 
                 3220 
               
               
                   
                 posterior surface 
                 3222 
               
               
                   
                 flexing region 
                 3230 
               
               
                   
                 left flexing region 
                 3232 
               
               
                   
                 right flexing region 
                 3234 
               
               
                   
                 decoupling region 
                 3236 
               
               
                   
                 plenum connection region 
                 3240 
               
               
                   
                 retaining structure 
                 3242 
               
               
                   
                 wide retention feature 
                 3244 
               
               
                   
                 narrow retention feature 
                 3245 
               
               
                   
                 barb 
                 3246 
               
               
                   
                 leading surface 
                 3246.1 
               
               
                   
                 trailing surface 
                 3246.2 
               
               
                   
                 additional surface 
                 3246.3 
               
               
                   
                 nominal vertical axis 
                 3246.4 
               
               
                   
                 sealing lip 
                 3250 
               
               
                   
                 pad printing 
                 3290 
               
               
                   
                 embossed text 
                 3291 
               
               
                   
                 recessed text 
                 3292 
               
               
                   
                 pad printing 
                 3293 
               
               
                   
                 ribs 
                 3294 
               
               
                   
                 notches 
                 3295 
               
               
                   
                 positioning and stabilising structure 
                 3300 
               
               
                   
                 strap 
                 3301 
               
               
                   
                 elastic tube 
                 3301.1 
               
               
                   
                 lock 
                 3301.2 
               
               
                   
                 loop portion 
                 3301.3 
               
               
                   
                 hook portion 
                 3301.4 
               
               
                   
                 end 
                 3301.5 
               
               
                   
                 rigidiser arm 
                 3302 
               
               
                   
                 distal free end 
                 3302.1 
               
               
                   
                 notch 
                 3302.2 
               
               
                   
                 extension arm 
                 3302.3 
               
               
                   
                 void 
                 3302.4 
               
               
                   
                 rod 
                 3302.5 
               
               
                   
                 raised stop 
                 3302.6 
               
               
                   
                 first slot 
                 3302.7 
               
               
                   
                 second slot 
                 3302.8 
               
               
                   
                 button-hole 
                 3303 
               
               
                   
                 attachment point 
                 3304 
               
               
                   
                 flexible joint 
                 3305 
               
               
                   
                 protruding end 
                 3306 
               
               
                   
                 sharp bend 
                 3307 
               
               
                   
                 opening 
                 3308 
               
               
                   
                 protrusion 
                 3309 
               
               
                   
                 frame 
                 3310 
               
               
                   
                 receiver 
                 3310.1 
               
               
                   
                 pocket 
                 3310.2 
               
               
                   
                 recess 
                 3310.3 
               
               
                   
                 indentation 
                 3310.4 
               
               
                   
                 end receiver 
                 3310.5 
               
               
                   
                 pocketed end 
                 3311 
               
               
                   
                 welded end 
                 3311.1 
               
               
                   
                 wide frame connection region 
                 3312 
               
               
                   
                 lead-in surface 
                 3312.1 
               
               
                   
                 retaining surface 
                 3312.2 
               
               
                   
                 narrow frame connection region 
                 3313 
               
               
                   
                 welded end 
                 3313.1 
               
               
                   
                 interfering portion 
                 3314 
               
               
                   
                 right side strap portion 
                 3315 
               
               
                   
                 left side strap portion 
                 3316 
               
               
                   
                 back strap 
                 3317 
               
               
                   
                 back strap portion 
                 3317a 
               
               
                   
                 back strap portion 
                 3317b 
               
               
                   
                 inner side of protrusion 
                 3318 
               
               
                   
                 outer side of protrusion 
                 3319 
               
               
                   
                 end of rigidiser arm 
                 3319a 
               
               
                   
                 end of rigidiser arm 
                 3319b 
               
               
                   
                 void of protrusion 
                 3320 
               
               
                   
                 top side of protrusion 
                 3321 
               
               
                   
                 marks 
                 3321a to 3321d 
               
               
                   
                 bottom side of protrusion 
                 3322 
               
               
                   
                 curved profile of rigidiser arm 
                 3323 
               
               
                   
                 marks 
                 3323a to 3323e 
               
               
                   
                 bifurcation point 
                 3324 
               
               
                   
                 reinforced portion 
                 3325 
               
               
                   
                 split region 
                 3326 
               
               
                   
                 reinforcement portion 
                 3327 
               
               
                   
                 rounded corners 
                 3328 
               
               
                   
                 recess of rigidiser arm 
                 3329 
               
               
                   
                 main section of rigidiser arm 
                 3333 
               
               
                   
                 opening of frame 
                 3335 
               
               
                   
                 first bend 
                 3340 
               
               
                   
                 first straight section 
                 3341 
               
               
                   
                 second bend 
                 3342 
               
               
                   
                 second straight section 
                 3343 
               
               
                   
                 locking end 
                 3344 
               
               
                   
                 slot 
                 3345 
               
               
                   
                 extension 
                 3350 
               
               
                   
                 end 
                 3350.1 
               
               
                   
                 straight section of extension 
                 3351 
               
               
                   
                 bend of extension 
                 3352 
               
               
                   
                 hook of extension 
                 3353 
               
               
                   
                 enclosable section of extension 
                 3354 
               
               
                   
                 outer surface of extension 
                 3355 
               
               
                   
                 joint 
                 3356 
               
               
                   
                 strap logo 
                 3357 
               
               
                   
                 indicia 
                 3358 
               
               
                   
                 flange 
                 3359 
               
               
                   
                 stem 
                 3361 
               
               
                   
                 first section of extension 
                 3363 
               
               
                   
                 second section of extension 
                 3364 
               
               
                   
                 first protrusion of second section 
                 3365 
               
               
                   
                 second protrusion of second section 
                 3366 
               
               
                   
                 first slot of second section 
                 3367 
               
               
                   
                 second slot of second section 
                 3368 
               
               
                   
                 extension 
                 3370 
               
               
                   
                 extension 
                 3371 
               
               
                   
                 indicia 
                 3372 
               
               
                   
                 joint 
                 3374 
               
               
                   
                 projection 
                 3380 
               
               
                   
                 wing 
                 3381 
               
               
                   
                 opening 
                 3382 
               
               
                   
                 notch 
                 3383 
               
               
                   
                 stop 
                 3384 
               
               
                   
                 pin 
                 3385 
               
               
                   
                 socket 
                 3386 
               
               
                   
                 flared end 
                 3387 
               
               
                   
                 receiver 
                 3388 
               
               
                   
                 slot 
                 3389 
               
               
                   
                 shaft receiver 
                 3390 
               
               
                   
                 arm receiver 
                 3391 
               
               
                   
                 slot 
                 3392 
               
               
                   
                 projection 
                 3393 
               
               
                   
                 arm 
                 3394 
               
               
                   
                 shaft 
                 3395 
               
               
                   
                 bend 
                 3396 
               
               
                   
                 protrusion 
                 3397 
               
               
                   
                 tab 
                 3398 
               
               
                   
                 column 
                 3399 
               
               
                   
                 vent 
                 3400 
               
               
                   
                 receiver 
                 3410 
               
               
                   
                 first magnet 
                 3412 
               
               
                   
                 post 
                 3411 
               
               
                   
                 second magnet 
                 3413 
               
               
                   
                 first L-shaped section 
                 3420 
               
               
                   
                 first recessed portion 
                 3421 
               
               
                   
                 first overlapping portion 
                 3422 
               
               
                   
                 second L-shaped section 
                 3423 
               
               
                   
                 second overlapping portion 
                 3424 
               
               
                   
                 second recessed portion 
                 3425 
               
               
                   
                 Peg 
                 3426 
               
               
                   
                 hole 
                 3427 
               
               
                   
                 boss 
                 3430 
               
               
                   
                 cavity 
                 3431 
               
               
                   
                 prong 
                 3450 
               
               
                   
                 hole 
                 3451 
               
               
                   
                 post 
                 3452 
               
               
                   
                 slot 
                 3453 
               
               
                   
                 rigidiser arm rib 
                 3460 
               
               
                   
                 extension rib 
                 3461 
               
               
                   
                 longitudinal rib 
                 3462 
               
               
                   
                 tab 
                 3470 
               
               
                   
                 hook material 
                 3471 
               
               
                   
                 connection port 
                 3600 
               
               
                   
                 PAP device 
                 4000 
               
               
                   
                 external housing 
                 4010 
               
               
                   
                 upper portion of the external housing 
                 4012 
               
               
                   
                 lower portion of the external housing 
                 4014 
               
               
                   
                 panel 
                 4015 
               
               
                   
                 chassis 
                 4016 
               
               
                   
                 handle 
                 4018 
               
               
                   
                 pneumatic block 
                 4020 
               
               
                   
                 pneumatic components 
                 4100 
               
               
                   
                 inlet air filter 
                 4112 
               
               
                   
                 controllable blower 
                 4142 
               
               
                   
                 air circuit 
                 4170 
               
               
                   
                 web of material 
                 4172 
               
               
                   
                 helical coil 
                 4174 
               
               
                   
                 inner portion of the bend 
                 4176 
               
               
                   
                 long tube 
                 4178 
               
               
                   
                 outer portion of the bend 
                 4179 
               
               
                   
                 short tube 
                 4180 
               
               
                   
                 humped portion 
                 4181 
               
               
                   
                 peak of the fold 
                 4182 
               
               
                   
                 slanted portion 
                 4183 
               
               
                   
                 outer surface of the helical coil 
                 4184 
               
               
                   
                 supplemental oxygen port 
                 4185 
               
               
                   
                 fold line 
                 4186 
               
               
                   
                 rotatable adapter 
                 4190 
               
               
                   
                 electrical components 
                 4200 
               
               
                   
                 printed circuit assembly (PCBA) 
                 4202 
               
               
                   
                 electrical power supply 
                 4210 
               
               
                   
                 input device 
                 4220 
               
               
                   
                 humidifier 
                 5000 
               
               
                   
                   
               
            
           
         
       
     
     PATENT LITERATURE 
     U.S. Pat. Nos. 7,743,767; 7,318,437; US patent publication 2009/0044808; WO publication 2000/069521; U.S. Pat. Nos. 5,724,965; 6,119,694. 6,823,869; US patent publication 2009/0044808; WO publication 2009/052560; WO publication 2005/010608; U.S. Pat. No. 4,782,832; WO publication 2002/11804; U.S. Pat. No. 6,854,465; US publication 2010/0000543; US publication 2009/0107508; WO publication 2011/121466; U.S. Pat. No. 7,562,658; EP patent 2,022,528; EP 1356841; US publication 2012/0318270; U.S. Pat. No. 8,439,038; US 2009/0078259; US publication 2009/0277525; US publication 2010/0224276; U.S. Pat. No. 6,581,594; US publication 2009/0050156; US2010/0319700; US publication 2009/0044810