Healthcare workers are at high risk of catching SARS‐CoV‐2 beca use of their regular interaction with patients with the disease. In lo w‐resource settings, the ratio of healthcare workers to the whole population is lower than in high income countries , and there is often limited access to personal protective equipment (PPE). Illness or death of healthcare work ers will, therefore, have a disproportionate impact in these settings, so it is particularl y important to find ways to protect them. To protect against airborne infe ction in healthcare settings, P PE recommendations typically include filtering facemask respirators o r powered air purifying respira tors (PAPR). The former, passively filter inhaled air. They are small, noiseless and do not require a pow er supply, but they are single‐use, presenting manufacturing and supply issues. Fit testing is cruc ial, and many users find them difficult to tolerate, due to breathing resistance and elevated humidity. There is also the potential for contamination due to the exposed face. PAPRs are re‐usable devi ces that may last for months and provide airflow through a filter from a battery‐powered blower unit to a hood or helmet which covers the face. This creates a positive pressure in the hood o r helmet that enables the wearer to breathe filtered air easily, with out requiring an air‐tight fit needed for standard face masks. This is reported to be more comfortable and provides better protection for the face from droplets and splashes, and infection by self‐ contact with the hands. PAPRs h ave typically been expensive, bulky and not readily available or easy to ship to low‐resource setti ngs. Although the design presented he re has not been through any for m of regulatory approval, the aim of this paper is to share ideas and offer possible solutions to other groups aroun d the World who may be thinking of manufacturing a low‐cost, reusable PAPR. The design is novel because it uses readily available materials, scala ble manufacturing processes, and it may be shipped flat‐packed and easily assembled. This offers an option for manufacturing in lo w‐resource settings and for shipping in bulk. This paper provides the CAD designs that can be fabricate d using a laser cutter. 1. INTRODUCTION The disease and its risks for low‐resource regions SARS‐CoV‐2 was classed as a global pandemic by the World Health Organization (WHO) on 11th March 2020 [1][2]. Infection resul ts in the clinical disease CO VID‐19, and can cause severe acute respiratory syndrome. Early in the pandemic, the healthcare sys tems of many high‐income countries were at capacity and close to bei ng overwhelmed, and the potent ial health, soci al and economic impacts of the pandemic on low‐r esource settings with lesser in frastructure and healthcare availability could be devastating and long‐lasting [3][4]. In l ow‐resource settings there is a greater risk that personal protective e quipment (PPE) has limited avail ability, and it is har der for individuals to self‐isolate because many of these countries have high popul ation density, larger household sizes and less support for people who lose their jobs or need time of f work [5][6][7]. The ratio of healthcare workers to the whole population is lower than in hig h income countries, and therefore sickness of healthcare workers can have a greater effect [8]. Staff in healthcare settings, in cluding medical staff, allied h ealth professionals, administrators and cleaners, have a high likelihood of catching SARS‐CoV‐2 because of their regular interaction with patients with the disease [9], a nd recurrent exposure may be as sociated with increased mortality [10]. Access to effective PPE fo r healthcare staff is vital, t o minimise the risks of catching symptomatic Covid‐19 or asymptoma tic onward transmission to pat ients, colleagues or families [11]. SARS‐CoV‐2 transmission routes The disease primarily spreads through droplet transmission when an infected person exhales, coughs, sneezes, or talks, and a susceptible person inhales aer osol droplets. People can also become infected by touching surfaces that have the virus on them, then touching their eyes, nose or mouth [12]. The SARS‐CoV‐2 virus is a pproximately in 50‐200 nm in dia meter [13]. However, it is not commonly transmitted as individual virions. It is transmitted, to varying degrees, as aerosol droplet nuclei (smaller than 5 μm diamete r), respiratory droplets (5‐10 μm diameter) and through fomites (via infected surfaces), with th e virus coming into contact wit h the body’s mucosal surfaces and airways through touch or re‐aero solisation [14]. Virus remains viable in fomites for varying times, from hours to days depending on the substrate, and lingers as a erosol, with a half‐life of 1.2 hours [15]. SARS‐CoV‐2 has been found to be present in faecal samples [16], and in toilets which have been used by COVID‐19 patients or where healthcare workers changed o ut of their personal protective equipment [17]. However, the presence of viral RNA does not nec essarily mean that viable virus is present, so the faecal‐oral/inha lation route has neither been c onfirmed nor ruled out. Current prevention measures For prevention of transmission, the WHO advises cleaning hands frequently with soap and water or alcohol‐based hand sanitiser, a nd avoiding contact with people coughing and sneezing [18]. Nevertheless, in countries where access to clean water is limit ed, even this basic precaution poses challenges [19]. A UNICEF and WH O joint study showed that 40% o f health care facilities are not equipped to practice hand hygien e at point of care, and 4 in 10 households do n ot have soap and water on premises. Many governme nts have also ad vised people to wear face coverings over the nose and mouth when outdoors or m eeting other people, to try to reduce the rate of infection [20], and this may reduce availability of PPE for healthcare workers. Types of PPE: N95/FFP2 face cov erings and PAPRs, advantages and disadvantages To protect against airborne infe ction for higher risk aerosol‐g enerating procedures (AGPs) in healthcare settings, PPE recomme ndations typically include two types of filtering devices: N95/FFP2 respirators (or N99/FFP3 as recom mended in the UK) and powered air purifying respirators (PAPR) [21] (see Table 1 for summary of common masks and respirators). The former passively filter inhaled air, requiring removal of 94% of aerosol particles (smaller tha n 5 μm in diameter) and droplets (5 μm to 50 μm), while allowing for ste thoscopes to be used, being no iseless and not requiring power supplies. However, these are reco mmended for single‐use, presen ting significant manufacturing, supply and logistic issues, and fi t testing is crucial for thei r optimal use and efficacy. Many users find them difficult to tolerate, due to breathing resistance and moi sture formation, and there is a potential for contamination due to the exposed face [21] [22]. On the other hand, PAPRs are re‐ usable devices that may last for months and provide airflow thr ough a filter from a battery‐powered blower unit to a hood or helmet which covers face. This creates a positive pressure in the hood or helmet that enables the wearer t o breathe filtered air easily, without requiring an air‐tight fit needed for standard face coverings. This is reported to be more comfortable and provides better protection for the face from dro plets and splashes, and infecti on by self‐contact w ith the hands [23]. PAPRs contain filters that are u sually housed as cartridges and can be interchanged according to the size and type of infection source. A typical filter used in PAP R is the high‐efficiency particulate air (HEPA) filter [24], which can f ilter at least 99.97% of particl es 0.3 μm in diameter, meaning that a HEPA filter‐equipped PAPR should provide greater protection tha n most N95/FFP2 respirators. PAPRs may be more inclusive, as they do not necessitate fit tes ting, and have other advantages, such as benefitting people with heari ng impairment who lip read, and improving commu nication, as patients can see doctors’ and nu rses’ faces [25] [26]. Addition ally, PAPRs are easier to wear for a long period of time, because fresh air flows on the user’s face and the avoidance of contact with skin on the face might avoid the sof t tissue discomfo rt and skin dam age experienced in FFPR use. However, they can be bulkier, no isier, and they require a power supply [21] [27], so they may not always be more usable and inclus ive than mask‐type respirators. Reusing fabric face coverings is not advisable because SARS‐CoV‐2 vir us survives for a long time on face covering material, so some organisations recommend that the y are disposed of after every u se, in a hospital context above all because not all of them are fit‐ tested meaning that there is an airflow leakage around the masks. However, cloth masks help protecting from large droplets especi ally when composed of different fabric layers [28] [29]. Overall, PAPRs offer better potential protection against respiratory pathogens, they can be cleaned and reused, and their filters can be substi tuted easily and safely [30] [31]. Technical specifications for per sonal respirators for health‐ca re workers are summa rised in a recent work by Elkington et al. [32]. Table 1 – Summary of common types of face coverings and respira tors. Filter efficiency, advantages and disadvantages are described for surgical masks, FFP type me dical masks and air purifying respirators. [33] [34] [35] [36] [37] [38] [3 9] [40] [41] [42] [43] [23] [44 ] [45] Novelty: low‐cost, easy to make and flat‐pack, easy to ship PAPRs have typically been expen sive and not as readily availabl e or as easy to ship to low‐resource settings as N95 respirators. There fore, this paper aims to prov ide an open‐source design for a PAPR prototype which can be made using low cost and off‐the‐shelf co mponents and materials, with common manufacturing techniques su ch as laser cutting and 3D pr inting. The objectives were to make it simple to assemble, easy to clean, flat‐pack for easy s hipping and functionally comparable to more expensive, commercially available respirators. 2. METHODS The presented prototype respirator is designed to provide prote ction for healthcare staff against COVID‐19 where respiratory prot ective equipment is not availabl e or prohibitively expensive, or where logistics make single‐use items impossible, both for supp ly and clinical waste handling. The Methods section covers the design requirements, materials and m anufacturing techniques used to create this prototype. The Results section provides the designs , with images and links to the CAD files, and the results of testing the prototype. Figure 1 – Flat‐pack PeRSo respirator with parts labelled. The prototype has been divided i nto 7 parts: the hood and visor ; the headband; the breather tube; the centrifugal fan, motor and battery; the filter and filter c ase; the connector; and the belt that holds the fan and electronics (F igure 1). For each part, the de sign aimed to meet the following specifications: ‐ flat or compact, prior to assembly, ‐ made of easily available, low‐cost materials, ‐ easy to manufacture (using a la ser cutter and a 3D printer), ‐ easy to assemble using common t ools such as glue and screwdrive rs, ‐ easy to clean and sterilise after each use, ‐ durable, efficient and meeting regulatory standards. CAD software was used to draw de signs (find them at the DOI pro vided above), and the prototype was built using a laser cutter (LS1690 PRO Laser, HPC Laser LTD ., UK; native software: Lasercut53) and a 3D printer (Ulti maker S5, Ultimaker). Specifications for each part: 1. Hood Design: The hood is designed to go over the whole head, covering the fa ce to protect the face from airborne droplets, splashes, and infection by self‐contact with the hands. This design means that the air flowing into the hood create s a positive pressure in the ho od that enables the wearer to breathe filtered air easily, without requi ring an air‐tight seal. This prevents the skin da mage that can be caused by pressure or rubbing of a seal against the skin. The d esign aims to be comfortable, lightweight and sound transmitting, with a clear panel across t he whole face so the wearer can see and communicate easily with patients and their family members a nd carers. It needs to be able to fit all face shapes comfortably. The hood also needs to be simple t o put on, take off and clean without spreading any virus that is present on the outside surface of i t. Materials, manufacturing and assembly: The materials used are propylene for the hood and transparent Tuftane thermoplastic polyurethane for the visor. A laser cutter is used both to cut the material and fuse the seams. Do uble sided tape is used to attac h the visor to the hood, and Velcro is used to attach the hood to the headband. 2. Headband Design: The headband supports the hood a nd the breather tube, so they can deliver the filtered air to the face. It also keeps the hood off the face. It needs to b e easily adjustable to fit the individual, so that the device is comfortabl e and stays in place. As part o f the headband, a diffuser spreads the flow of the air from the breathe r tube more evenly across the f ace. Materials, manufacturing and assembly: Polypropylene sheet is cut to shape using a laser cutter, and Velcro is used to attach it to the hood. The headband slots together and features adjustable bands for resizing. 3. Breather tube Design: a breather tube is required to t ransport the filtered air from the fan to the hood, because the weight of the fan and battery is more comfortable to wear o n the back or the waist, rather than on the head. It is therefore a requirement that the breather tu be is lightweight and flexible, so it does not limit the movements of the wearer. Materials, manufacturing and assembly: Any type of medical grade tube can be used. In order to have the most flexibility, this pr ototype breather tube is made out of a common spiral cable tidy and covered in lay‐flat polypropylene tubing. 4. Centrifugal fan, motor and batteries Design: The fan consists of impeller plates and blades, along with a c ase; a brushless motor and case; and screws. Ideally, the battery s hould enable the device to po wer for 8 hours, or the standard length of a healthcare worker’s shift. However, if the device d oes not meet this requirement, it is easy to change over the batteries when they are getting low. Materials, manufacturing and assembly: This prototype uses a dro ne motor (A2212/6T 2200KV ‐ operating voltage: 7.2V to 12V w ith no load current: 0.5 A). Th e centrifugal fan is laser cut, and the case for the motor is 3D printed. This prototype uses 6 recharg eable NiMh, 1.2 V, 1300 mAh AA batteries (Duracell). 5. Filter and filter case Design: The filter needs to remove viru s participles from the air and be easily replaceable if it gets damaged or clogged up. The filter case needs to protect the fil ter and be easy to clean. Materials, manufacturing and assembly: This prototype uses a HEPA‐FLO NVM‐1CH (Numatic International) filter and the filter case is made out of laser cut Perspex, covered in polypropylene for easy cleaning. 6. Connector Design: A connector is required to link the air output f rom the centri fugal fan to the breather tube. There needs to be an airtight se al at the entrance to the breat her tube, so unfiltered air does not enter the breather tube and the filtered air efficiently reache s the hood. Materials, manufacturing and assembly: The connectors are laser cut out of polypropylene and sealed with duct tape. 7. Belt Design: The belt is designed to hold the fan and the electronics in an ergonomic manner suitable for healthcare workers. It is designed to be easy to access the int ernal parts, easy to clean, and have size‐adjustable straps for the waist. Materials, manufacturing and assembly: The belt is made out of laser cut out of polypropylene and the pieces slot together. Testing the prototype Initial testing was performed on the prototype to test that its battery life was suitable for a full health‐worker shift length, the airflow rate was fast enough fo r the wearer to breathe easily and to have no CO 2 build‐up in the hood, and to che ck the sealing of components. a) Battery life A commercial floating ball flowme ter was used to assess the flo w rate of the fabricated fan in outlet after mounting it with the HEPA filter material. A small sectio n of hose (26 mm internal diameter, Part no. CUXS10, Griflex, Birmi ngham, UK) was used to connect t he fan to the flowmeter. Flow rate was kept at 165 L/min [46], incr easing the voltage over time to ensure ideal flow rate would reach the hood through the breather tube. b) Flowmeter test An anemometer (Kestrel 5200 Prof essional Weather Meter 0852LHVG , Kestrel Meters, USA) was employed to test the flow rate o f the assembled fan with the el ectronics mentioned above. c) Nebuliser bitter test to check sealing of components Commercially available nebuliser a nd test solutions (FT‐30 & FT ‐32 solution and spray apparatus, 3M UK, St Paul, MN, USA) were employed to ensure acceptable positi ve pressure inside hood, particulate efficacy of filter, and sealing around assembly. Th e bitter solution was sprayed 30 times directly in front of the visor while the users wearing the resp irators performed simple actions such as breathing normally, breathing heavily, tilting the head left /right and up/down, talking and bending. During these tests, a use r wearing the respirator shou ld not taste or smell the atomised bitter solution. As a positive co ntrol, the solution was spraye d close to the users’ face to ensure sensibility to the compound. 3. RESULTS Hood The hood polypropylene was sourced from standard rubble bags (5 08 mm x 762 mm from Polystar Plastics Ltd, UK). The transparent rubble bag (effectively two layers of polypropylene sheets sealed at the long edges and at one short edge) was placed on the bed of the laser cutter and the laser was focussed at a height of 40 mm (this value depends on the machin e employed). This height, which changes according to the different machines available, is optim al for a well‐focused laser which can cut the chosen material, in spec ific areas. Figure 2 shows the hood and visor pattern. The black lines were cut with a speed of 150% a nd a power of 50% (Figure 2.A, b lack lines). After this step, the laser cutter was also used to cut and seal the blue lines on the hood . The laser was move d out of focus at a height of 60 mm above the rubbl e bag. The cut and seal proces s was achieved wit h a speed of 20% and a power of 25% (Figure 2.A, blue lines). To make the visor, a 0.5 mm thic k sheet of transparent Tuftane thermoplastic polyurethane (TPU) was laser cut to fit the region of hood corresponding to the fa ce. TPU was cut with a speed of 50% and a power of 30% (Figure 2.B). Then the Tuftane visor was att ached internally to the rubble bag hood with double sided tape to ensure the sealing. Figure 2.C s hows the assembled hood and Figure S 1 shows the laser cutti ng process of the hood. Figure 2 ‐ Hood from rubble bag. A) side design of hood to be l aser cut from rubble bag. Black lines are to be cut, and leave open features or edges, whereas blue lines are to be cut and sealed, creating a seam; B) visor design to be cut and taped to the upper opening of the hood; C) complete fabricated hood design with visor. Headband The headband was fabricated by laser cutting of 0.75 mm thick p olypropylene sheet. The headband was designed to be easy to assemble without requiring further p arts or tools. It is made of three parts: (i) a strip which when a ssembled goes on the sides of th e head and comprises an air diffuser on the forehead. The ends are designed as a series of inverted Us which then lock into a back plate (Figure 3.A); (ii) a strip to ho ld the headgear from sliding do wn and to hold the breather tube in position (Figure 3.B); and (iii) a back plate which has a recta ngular shape with small slots that can fit the strips in order to adjust th e size of the headband on the s ides and on the top of the head (Figure 3.C). This allows for the headba nd to be easily adjusted to hea d sizes spanning from 480 mm to 640 mm in circumference (or different sizes when editing the design provided). The part was laser cut with a speed of 75%, a power of 100% and a corner power of 30%. Figure 3.D shows the complete headband. Figure S 2 and Video 1 show the assembling process. Figure 3 – Headband to hold hood and breather tube on user’s he ad. A) T‐shaped strip that goes around the sides of the head, contains the PeRSo shaped diffuse r and joins with (B) and (C) to form the complete headband; B) top strip to hold the breather tube that connects to (A) thr ough (C); C) back plate with vertical slots for (A ) and horizontal slots for (B); D) the assembled headband. Breather tube The breather tube has an external diameter of 30 mm and interna l diameter of 28 mm. It was made out of common spiral cable tidy (30 mm external diameter) and c overed in lay flat tubing (polypropylene, 2” x 500 gauge) (see Figure 4). The tube length can be tailored to the height of the user; however, a length of 120 mm is appropriate for most users ranging from 1.60 m to 1.90 m in height. This results in a very d eformable and light breather tu be that allows for air flow to travel from fan to hood. Figure 4 – The breather tube, m ade of spiral cable tidy and cov ered in polypropylene lay‐flat tubing. The breather tube was glued in po sition at the top part of the headband by the headgear side straps and its outlet flows onto the di ffuser at the forehead. Then th e headband was attached inside the hood using Velcro straps. Figure S 3‐left shows the upper part of the respirator which consists of hood, headband and breather tube. The total weight of the upper part was 150 g. Centrifugal fan and motor The centrifugal fan has the following components: 1. Fan case: made of laser cut Pers pex (3 mm thick) (Figure 5.A) a nd laser cut polypropylene (0.75 mm thick) (Figure 5.D) 2. Impeller plates: laser cut out of Perspex (3 mm thick) (Figure 5.B) 3. Impeller blades (18): laser cut out of polypropylene (0.75 mm t hick) (Figure 5.C) 4. Brushless motor (off‐the‐shelf dr one motor) and 3D printed case (Figure 5.G‐frame). 5. M4 screws for fan case, M3 screw s for impeller, M3 screws for m otor case. The laser cutter settings for the Perspex were: speed 40%, powe r 100% (cut twice); for engraving (red in Figure 5.A) offset 0.2 mm (x6) speed 50%, power 20%. La ser cutter settings for polypropylene: speed 75%, power 100%, corner power 30%. Figure 5 ‐ Centrifugal fan assembly with off‐the‐shelf drone mo tor. A) top plate (left) with opening for air intake, and back plate (right) with holes for motor screws and spindle. Red lines show the path in which the wall strip in (D) locks ; B) impeller plates with slot s for blades, and holes to hold motor case so that the impeller spins with the motor; C) impeller blades; D) strip locking into red path in (A) which encloses the impeller; (E) laser‐cut parts for centrifugal fan are (F) assembled using hot glue. The top fan plate is attached to the back assembly using screws for eas y access to drone motor; (G) assembly of centrifugal fan with drone motor, battery pack and controller c onnected to it. The controller has a I/O switch and a wheel to control the voltage supplied to the fan. The green frame shows the assembly of the drone motor in the 3D printed holder which connects to the impeller to allow rotation. The brushless drone motor (A2212/ 6T 2200KV ‐ operating voltage: 7.2V to 12V with no load current: 0.5 A), was connected to a speed regulator controller (Part ID: Keensonvqgo3z9sw, CS Priority Industrial Ltd, China) which is a lso connected to 6 AA batterie s (7.2 V total). The controller has a potentiometer that can be turned to adjust the voltage provided to the motor and hence the flow rate going into the hood. In order to connect the motor to the fan case, a motor case was designed, and 3D printed. The 3D printing settings were: infill 60%, laye r height 0.2 mm, adhesion, no support. Video 2 shows the assembling of the centrifugal fan. However, 3D printing can be avoid ed if the drone motor is equip ped with an integrated screw on top of the spindle that can be ancho red through a nut to the impell er. This would result in the whole respirator being manufactured just by laser cutting, which make s the process much faster than 3D printing. Once the fan parts were laser cut, the fan back plate was hot g lued to the wall strip, and the impeller blades were glued to the plates (Figure 5.E‐F). The top casing plate was connected to the back assembly by 6 M3 screws for easy access to the motor. The drone motor was placed into the 3D printed holder (green frame in Fi gure 5.G) and this was secured to the back impeller plate, whereas the drone motor was attached to the fan back plate by M2 screws (supplied with the motor) going into the drone motor body. Then, the motor was connected to the controller and the battery pack. Filter and filter case The filter case was mounted outs ide the fan so that the air tha t is drawn first through the filter for purification, then into the fan, and blown into the breather tu be and into the hood. The filter case was made out of laser cut Perspe x (Figure 6.A) and covered with laser cut 0.75 mm thick polypropylene (Figure 6.B) t hat can be easily cleaned. Filter medium of choice was HEPA material from vacuum bags (HEP A‐FLO NVM‐1CH, Numatic International), which was wetted before being laser cut (speed 100%, power 30%) (Figure 6.C). Figure 6 ‐ Filter case with HEPA filter. A) clockwise from top left: i) ring to hold filt er material, ii) ring to support filter material, iii) bac k plate to hold filter in plac e, iv) side plates for filt er cartridge; B) cover for filter cartridge for easy cleaning and protection from spil ls and droplets; C) cut design for filter material of choice; D) component s for filter case. Rubber O‐rin gs and rubber washers were used to ensure sealing of the assembly; E) assembled filter case on the left with cover on the right. The filter case was assembled to ensure sealing of all componen ts (Figure 6.D) so that the air flowing into the fan would be completely filtered before going into the breather tube. A large O‐ring was positioned on top of the fan case, then the next layer was the cut‐out Perspex ring with six holes for screws inside, followed by a sma ller O‐ring and the back plate to support the filter. Then the filter material and the plate for the fan cover were placed on top of the assembly and rubber washers were aligned to the 6 holes. Thes e were held in place by 6 scre ws (left in Figure 6.E). For the fan cover, the side Pers pex plates were then attached t o the polypropylene sheet through pins and slots respectively (ri ght in Figure 6.E). The assemble d filter cover then slides into the back‐ filter cover on the first assemb ly and it is held in place secu rely by two pairs of p ins and slots in the back plate and the filter cover respectively. This ensures that the filter case is well sealed and allows for easy cleaning of the fan system. Video 3 shows the assemb ling of the filter case. Connector A connector was designed to attac h the fan and th e hood to the breather tube. The connector was laser cut out of polypropylene (speed 75%, power 100%, corner p ower 30%) and has a pyramidal shape connecting the outlet of the fan to the inlet of the brea ther tube (Figure 7.A). The design allows for connection to differe nt size tubes. The assembled co nnector is shown in Figure 7.B and it was later sealed with duct tape t o the fan case and the breathe r tube to make the system airtight. Figure 7 – Connector for breather tube to centrifugal fan. A) D esign; B) Laser‐cut and assembled connector. Belt The belt was made out of laser cut 0.75 mm thick polypropylene (speed: 75%, power: 100%, corner power: 30%). The belt has a larg e plate to support (i) the fan, through 6 screws which are used to hold the fan case (Figure 8.A), (ii) the controller, that is mo unted at the upper edge of the belt for easy access, and (iii) the battery pack, mounted in a pocket (F igure 8.B). The straps (Figure 8.D) interlock in a frontal plate with slots and can be adjusted acc ording to user’s waist (Figure 8.C). Figure 8 – Belt to hold the blower units with the electronics. A) belt back plate holding battery pack on the left and centrifugal fan on the right via the 6 screws in t he fan case; B) strip holding battery pack. This connects to the horizontal slots in (A); C) front plate wi th slots to lock the waist strips (D) with U‐ shaped features to allow for different lengths to be chosen acc ording to user’s waistline; E) fabricated belt. The belt was assembled as shown i n Figure 8.E. The blower unit containing the electronics (battery pack and controller) and the fan connected to the belt is shown in Figure S 3‐right. The controller allows the voltage supplied to t he fan to be adjusted, by rotat ing the switch, which modifies the flow rate. The total weight of the blower unit is 600 g. 3.1.6 Final prototype Figure 1 shows the final prototype, connecting the hood‐headban d‐breather tube upper assembly to the connector‐blower unit‐electronics‐belt lower assembly. The prototype has a clean, simple and light appearance. Such a design, as showed previously by Elking ton et al. 2020 [32] results in a friendly look, helping people to see each other’s face and comm unicate easily. The total cost of the materials used in this prototype was ~£50 , which makes it a low‐cost device. The total weight is 750 g and it occupies a volume of 300 mm (L ) x 300 mm (W) x 8 mm (D) when assembled and stored. Video 4 shows the demonstration of a fully developed prototype. 3.2 Flow rate, battery life and sealing tests The flow rate of the drone motor and flat‐pack fan was tested a t 7.2 V and at the f an outlet a flow rate of 190 L/min was recorded. Pr e‐use testing wi th an anemome ter prototype ma y be useful to ensure that the flow is sufficient for the usage. Flow may vary because of battery degradation or tube length adjustment, therefor e checking the flow before sett ing up the device is recommended. The performance of the assembled blower unit in terms of batter y life was tested by using a floating ball flowmeter. The motor was switched on and the fan was contr olled manually so that the flowmeter indicated 165 L/min, f or as long as the battery charg e allowed. Using 6 NiMh, 1.2 V, 1300 mAh AA batteries, the fan was ab le to deliver 165 L/min for 2 h ours and 45 minutes. Increasing the total current supplied (i.e. the number of batteries connected in parallel) will consequently enhance the battery life of the device. Using a power supply such as a power bank or battery packs equipped with LEDs may be helpful to see the charge level and understand the remaining run time of the power supply. Additionally, the full prototype was fit tested by using a bitt er solution atomised via a nebuliser. Users could not taste the solution when wearing the respirators and while performing different tasks, meaning that the hood properly seals the head. As a posi tive control, users could taste the bitter solution when not wearing the flat‐pack respirator. 4. DISCUSSION The results demonstrate the fe asibility of designing and buildi ng a low‐cost PAPR using off‐the‐shelf components, laser cutting and 3D printing. The paper provides d etailed information on how to build this simple, flat‐pack design. I nitial tests suggest that this design has comparable efficacy with more expensive, commercially available respirators. Moreover, the ma terials used are selected for easy cleaning and sterilisation after every use. The filter case is also designed so that it can work as a cartridge, and different filter media can be integrated in the respirator. With SARS‐CoV‐2 spreading rapidly in low‐resource settings, hea lthcare systems are strained in both staffing and infrastructure. Th e chronic supply issues related to disposable PPE are acutely compounded by the coronavirus pa ndemic and associated economic disruption. Increased mortality amongst healthcare wor kers has already been observed in high in come countries [3][4], so it is vital that PPE is adequate and available to protect the healthcare wo rkers in low‐resourced settings, where there are shortages of hea lthcare workers. Recent UK data also indicates the greatest risk of infection in Black and Asian healthcare workers, irrespective o f their working location, but this may due to the types of employment they hold, their greater relianc e on public transport and living in multigenerational or large house holds, compared to their white British counterparts, rather than a genetic disposition [47]. It is important to remember to provid e protection for a ll people who work in healthcare settings, including cleaners and administrators, not only clinicians, and to consider how to protect people on t heir commute to work. Proper protocols need to be put i n place for wearing, removing and cleaning the respirators as well, because the virus that the respi rator protects workers from is likely to land on the outside surface of the respirator, so needs to be re moved with care to stop the vi rus from spreading to the wearer’s hands and face [32]. PAPRs represent an alternative strategy to standard filtering f ace covering PPE t hat may have particular benefits for low‐reso urce settings. Firstly, one reu sable PAPR device can replace the months‐long requirement of facema sk respirators, visors and cap s or, realistically, avoid the risks of re‐using these single‐use device s out of necessity. Secondly, h ealthcare staff will be more efficient, able to move from patient to pat ient without repetitively chang ing their PPE. Thirdly, as the whole face can be seen in a PAPR, comm unication is eas ier than with s ingle‐use face coverings, and finally, PAPRs may be more comfortable th an a tight‐fitting face coverin g in hot climates because of the cool air flow reducing sweat build‐up, and avoidance of loading the face’s vulnerable soft tissues. However, the PAPR design has some limitations. It can be more r estricting of movement, due to being bulkier than a single‐use face covering, and because it c overs the ears and has a fan, it can be harder to hear through it and to use a stethoscope. It is there fore useful to prioritise a low‐noise fan, to direct the flow of air away f rom the ears, and to use materi als that are not noise‐insulating. The addition of sensors and warning alarms to alert the wearer if t he battery is low or the flow rate from the fan has decreased beyond the recommended levels, can be use ful for making sure the healthcare workers remain protected throughout the day. Often commercially available PAPR s are much higher specificatio n than required for healthcare use, as they are designed for industries such as welding. Therefore, we developed a cheap and simple respirator. The components are d eliberately suitable for mass p roduction and often repurposed from other widely available source s. The designs are presented in full, to support in‐country manufacture. They are available open source, with no intellectu al property protection and all data on the manufacture process is published online. In the present work, we have avoided direct reverse‐engineering, and are not aware of any intellectual prop erty conflicts. However, we have not undertaken a full international freedom to operate search, so w e recommend that manufacturers using this design run an indepen dent intellectual property sear ch to make sure there are no infringements. In the case of infringements, governments may be able to invoke legislation like Crown Use Exemption to authorise use of IP without the owner’s agreement, or the World Trade Organisation’s Agreement on Trade Related Aspects of Intellectu al Property Rights, but individuals should be aware of the legal risks of infringement. Local checks and regulatory appro val will be needed to confirm the efficacy of respirators after manufacture, such as checking fo r ingress around the filter usi ng the spray test solutions. We will provide technical updates on our website and aim to develop this as a community of practice, showing different potential manufacturing solutions suitable fo r different geographic settings. We propose that widespread manufactu ring and use of PAPRs may redu ce the impact of the SARS‐CoV‐2 pandemic, both short and long term, by enabling more effective healthcare provision and keeping staff safe to care for others. Acknowledgements We would like to acknowledge the support of the PeRSo‐DW team members: Ric Gillams, Alexandra Mant, David Marshall, Hywel Mor gan, Philippa Reed, Clint Styles and Liku Tezera; and the Institute for Life Sciences (IfLS) for i nitiating our collaboration. We thank Chris Malcolm from the Design Workshop at the Universi ty of Southampton for his support with the equipment needed for the fabrication of the pr ototype, and Dan Edmunds from Permali Gloucester Ltd for supplying Tuftane material used for the visors. We gratefully acknowledge support from the University of Southa mpton Strategic Development Fund, which is funded by the UK Go vernment as part of the Globa l Challenges Research Fund (GCRF), and projects that seconded staff to this work including MRC (MR /P023754/1 (PTE)), EPSRC (EP/L025035/1 (ADG) and EP/R014213/1 (ASD, LED)), and donations to the Southampton Coronavirus Response Fund. We th ank Action 4 Equality (Scotland ) Limited (Dr Alison Steele and Mr Stefan Cross, QC) for the gift pr ovided to support this researc h. Additional data has been made op enly available from the Univers ity of Southampton repository at https://doi.org/ 10.5258/SOTON/D1582 .