Patent Publication Number: US-2020281258-A1

Title: A Filter Unit for a Smoking Article

Description:
TECHNICAL FIELD 
     The present invention relates to a filter unit for a smoking article, a smoking article including such a filter unit and a kit of parts comprising a smoking article and a filter unit. 
     BACKGROUND 
     Cigarettes and other smoking articles produce an aerosol, such as smoke in the case of cigarettes, which is inhaled by a user. A filter may be provided as part of a smoking article, or can be provided as a separate component which can be attached or coupled to a smoking article by a user. Filters can be configured to modify properties of aerosol produced by the smoking article; for example, by adding flavourant to the aerosol produced by the smoking article. 
     SUMMARY 
     According to embodiments of a first aspect of the invention, there is provided a filter unit for a smoking article comprising a tube formed from filter material and having a first portion and a second portion, wherein an inner diameter of the first portion is different from an inner diameter of the second portion. 
     The second portion can be at a distal end of the filter unit. 
     The inner diameter of the second portion can decrease with distance from the distal end of the filter unit. 
     The inner diameter of at least part of the second portion can be greater than the inner diameter of the first portion. 
     An outer diameter of the second portion can be substantially the same as an outer diameter of the first portion. 
     The second portion can include a chamfer resulting in the inner diameter of at least part of the second portion being greater than the inner diameter of the first portion. 
     Each of the first portion and the second portion can have a respective first and second end, and the second end of the first portion can adjoin the first end of the second portion and can have an inner diameter substantially the same as the first end of the second portion. 
     According to embodiments of a second aspect of the invention, there is provided a filter unit for a smoking article comprising a tube formed from filter material and having a longitudinal axis, wherein a straight line following at least a portion of an internal or external surface of the tube intersects the longitudinal axis at an angle other than 90°. 
     The straight line can comprise a first straight line following a first portion of the internal or external surface of the tube and wherein a second straight line following a second portion of the internal or external surface of the tube is parallel to the longitudinal axis. The angle can be between about 20° and about 70°, and/or between about 30° and about 60° and/or between about 35° and about 55° and/or is about 45°. Said internal or external surface of the tube can be adjacent to a longitudinal end surface of the tube. 
     The filter unit can further comprise a sleeve and a cylindrical element, wherein the sleeve can at least partially surround each of the tube and the cylindrical element. 
     The cylindrical element can be formed from filter material. The cylindrical element can comprise a body having an end surface adjacent to the tube and a recess formed in the end surface. 
     A smallest internal diameter of the tube of the first or second aspects can be between about 1 mm and about 5 mm and/or between about 1.5 mm and about 4.5 mm, and/or between about 2 mm and about 4 mm, and or about 3 mm. 
     According to embodiments of a third aspect of the invention, there is provided a filter unit for a smoking article comprising a body or tube of filter material having a longitudinal axis, a first end surface and a second end surface, said body or tube formed from a plurality of continuous fibres extending between said first and second end surfaces, wherein the density of said filter material is greater at said first end surface than at said second end surface. 
     According to embodiments of a fourth aspect of the invention, there is provided a filter unit for a smoking article comprising a body of filter material having a longitudinal axis and a channel or recess formed in the body of filter material, the shape of said body of filter material having no lines of reflective symmetry. 
     According to embodiments of a fifth aspect of the invention, there is provided a filter unit comprising a body formed from filter material, the body having an end surface and a recess formed in the end surface. 
     The recess can comprise a base surface and at least one side surface. 
     The recess can be substantially cylindrical, conical or hemispherical in shape or the shape of the recess can have order 1, 2, 3, 4, 5, 6, 7, 8, or continuous rotational symmetry. 
     The filter material at a surface of the recess can be denser than the filter material at the end surface of the body. 
     The body can be cylindrical and can have a longitudinal axis and the end surface can be a longitudinal end surface of the body substantially perpendicular to the longitudinal axis. 
     The filter unit can further comprise a sleeve at least partially surrounding the body. 
     The filter unit can further comprise a smoke modifying substance disposed within the filter material of the body. 
     The smoke modifying substance can comprise an encapsulated substance. 
     The filter unit set out above can be arranged to be coupled to a smoking article by a user. 
     The filter unit can comprise between 12% and 25% by weight plasticiser in the filter material and/or between 16% and 19% plasticiser. The filter material can comprise cellulose acetate and said plasticiser can comprise triacetin. 
     The filter unit can have a hardness of between 85% and 95% and/or between 88% and 94%. 
     The filter material can comprise filter tow with a denier per filament of from 3 to 15 or from 4 and 8 and a total denier of from 15,000 to 40,000 or from 30,000 to 40,000. 
     According to embodiments of the invention, there is also provided a smoking article comprising a filter unit as set out above. 
     The second portion of the tube can be disposed at a mouth end of the smoking article. 
     The end surface of the body can be disposed at a mouth end of the smoking article. 
     According to embodiments of the invention, there is provided a kit comprising a smoking article and a filter unit as set out above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1 a    is a side-on cross sectional view of a first filter unit including a tube formed from filter material and where the filter unit forms part of a smoking article; 
         FIG. 1 b    is a side-on cross sectional view of an outer chamfered tube for use as an alternative to the tube used in the first filter unit of  FIG. 1   a;    
         FIG. 1 c    is a further side-on cross sectional view of the tube formed from filter material of  FIG. 1   a;    
         FIG. 1 d    is a further side-on cross sectional view of the outer chamfered tube of  FIG. 1   b;    
         FIG. 1 e    is a side-on cross sectional view of a filter insert for use with the first filter unit of  FIG. 1   a;    
         FIG. 2  is a side-on cross sectional view of a second filter unit including a tube formed from filter material and where the filter unit is provided as a discrete unit for use with a separate smoking article; 
         FIG. 3 a    is a side-on cross sectional view of a third filter unit including a filter body comprising a recess and where the third filter unit forms part of a smoking article; 
         FIG. 3 b    is an end-on view of the third filter unit of  FIG. 3   a;    
         FIG. 3 c    is an end-on view of another third filter unit design, this design having a triangular shaped recess; 
         FIG. 3 d    is an end-on view of another third filter unit design, this design having a hexagonal shaped recess; 
         FIG. 3 e    is an end-on view of another third filter unit design, this design having a substantially cone shaped recess; 
         FIG. 3 e   ′ is a side-on cross sectional view of the third filter unit design of  FIG. 3   e;    
         FIG. 3 f    is an end-on view of another third filter unit design, this design having a recess having a first portion in the form of a frustum cone, a second portion in the form of a cylinder and a third portion in the form of a cone; 
         FIG. 3 f    is a side-on cross sectional view of the third filter unit design of  FIG. 3   f;    
         FIG. 3 g    is an end-on view of another third filter unit design, this design having a recess having a first portion in the form of a cylinder and a second portion in the form of a cone; 
         FIG. 3 g   ′ is a side-on cross sectional view of the third filter unit design of  FIG. 3   g;    
         FIG. 3 h    is an end-on view of another third filter unit design, this design having a recess in the form of a rhomboid prism; 
         FIG. 3 h   ′ is a side-on cross sectional view of the third filter unit design of  FIG. 3   h;    
         FIG. 3 i    is an end-on view of another third filter unit design, this design having a recess in the form of the capital letter ‘L’; 
         FIG. 3 i   ′ is a side-on cross sectional view of the third filter unit design of  FIG. 3   i;    
         FIG. 3 j    is an end-on view of another third filter unit design, this design having a recess in the form of the capital letter ‘Y’; 
         FIG. 3 j   ′ is a side-on cross sectional view of the third filter unit design of  FIG. 3   j;    
         FIG. 4  is a side-on cross sectional view of a fourth filter unit including a tube formed from sheet material and provided as a discrete component for use with a separate smoking article; 
         FIGS. 5 a  to 5 d    are perspective views of an apparatus for shaping a tobacco industry product; 
         FIGS. 6 a  to 6 i    are side-on views of respective first to ninth shaping heads for use with the apparatus of  FIGS. 5 a  to 5 d   , the side on views being from the direction of the respective arrows of  FIGS. 6 a   ′ to  6   i′;    
         FIGS. 6 a   ′ to  6   i ′ are end-on views of the respective first to ninth shaping heads of  FIGS. 6 a    to  6   i;    
         FIG. 7  is a flow diagram illustrating a method of shaping a tobacco industry product; and 
         FIG. 8  is a flow diagram illustrating a method of shaping a tobacco industry product. 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, the term “tobacco industry product” is intended to include smoking articles comprising combustible smoking articles and their components such as cigarettes, cigarillos, cigars, tobacco for pipes or for roll-your-own cigarettes, (whether based on tobacco, tobacco derivatives, expanded tobacco, reconstituted tobacco, tobacco substitutes or other smokable material), electronic smoking articles and their components such as e-cigarettes, heating devices that release compounds from substrate materials without burning such as tobacco heating products, and hybrid systems to generate aerosol from a combination of substrate materials, for example hybrid systems containing a liquid or gel or solid substrate; and aerosol-free nicotine delivery articles and their components such as lozenges, gums, patches, articles comprising breathable powders and smokeless tobacco products such as snus and snuff. Components of the above articles include filter units, filter plugs, filter inserts and tubes for use in products such as smoking articles; 
     In one embodiment, the tobacco industry product is a smoking article for combustion, selected from the group consisting of a cigarette, a cigarillo and a cigar. 
     In one embodiment, the tobacco industry product is a non-combustible smoking article. 
     In one embodiment, the tobacco industry product is a heating device which releases compounds by heating, but not burning, a substrate material. The material may be for example tobacco or other non-tobacco products, which may or may not contain nicotine. In one embodiment, the heating device is a tobacco heating device. 
     In one embodiment, the tobacco industry product is a hybrid system to generate aerosol by heating, but not burning, a combination of substrate materials. The substrate materials may comprise for example solid, liquid or gel which may or may not contain nicotine. In one embodiment, the hybrid system comprises a liquid or gel substrate and a solid substrate. The solid substrate may be for example tobacco or other non-tobacco products, which may or may not contain nicotine. In one embodiment, the hybrid system comprises a liquid or gel substrate and tobacco. Filter units described herein can be provided to users as an integral component of a smoking article or as a discrete component separate from a smoking article. When provided separately, filter units and smoking articles can be packaged separately, or packaged together as a kit of parts. 
     Smoking articles such as cigarettes and their formats are often named according to the cigarette length: “regular” (typically in the range 68-75 mm, e.g. from about 68 mm to about 72 mm), “short” or “mini” (68 mm or less), “king-size” (typically in the range 75-91 mm, e.g. from about 79 mm to about 88 mm), “long” or “super-king” (typically in the range 91-105 mm, e.g. from about 94 mm to about 101 mm) and “ultra-long” (typically in the range from about 110 mm to about 121 mm). 
     They are also named according to the cigarette circumference: “regular” (about 23-25 mm), “wide” (greater than 25 mm), “slim” (about 22-23 mm), “demi-slim” (about 19-22 mm), “super-slim” (about 16-19 mm), and “micro-slim” (less than about 16 mm). Accordingly, a cigarette in a king-size, super-slim format will, for example, have a length of about 83 mm and a circumference of about 17 mm. Cigarettes in the regular, king-size format are preferred by many customers, namely with a circumference of from 23 to 25 mm and an overall length of from 75 to 91 mm. 
     Each format may be produced with filters of different lengths, smaller filters being generally used in formats of smaller lengths and circumferences. Typically the filter length will be from about 15 mm, associated with short, regular formats, to 30 mm, associated with ultra-long super-slim formats. The tipping paper will have a greater length than the filter, for example from 3 to 10 mm longer, such that the tipping paper covers the filter and overlaps the tobacco rod to connect the filter to the tobacco rod. 
     Smoking articles and filter units described herein can be made in, but are not limited to, any of the above formats. 
     The filter material forming any of the filter units or other filter components described herein can comprise cellulose acetate fibre tow. The filter material can also be formed using other materials used to form fibres, such as polyvinyl alcohol (PVOH), polylactic acid (PLA), polycaprolactone (PCL), poly(1-4 butanediol succinate) (PBS), poly(butylene adipate-co-terephthalate)(PBAT), starch based materials, paper, cotton, aliphatic polyester materials and polysaccharide polymers or a combination thereof. The filter material may be plasticised with a suitable plasticiser for the filter material, such as triacetin where the filter material is cellulose acetate tow, or may be non-plasticised. The tow used to produce the filter unit or other filter component can use any suitable specification, such as fibres having a ‘Y’ shaped or other cross section, filamentary denier values between 2.5 and 15 denier per filament, for example between 3.0 and 9.0 denier per filament and total denier values of 10,000 to 50,000, for example between 15,000 and 45,000. 
     As used herein, the terms “flavour” and “flavourant” refer to materials which, where local regulations permit, may be used to create a desired taste or aroma in a product for adult consumers. They may include extracts (e.g., liquorice, hydrangea, Japanese white bark magnolia leaf, chamomile, fenugreek, clove, menthol, Japanese mint, aniseed, cinnamon, herb, wintergreen, cherry, berry, peach, apple, Drambuie, bourbon, scotch, whiskey, spearmint, peppermint, lavender, cardamom, celery, cascarilla, nutmeg, sandalwood, bergamot, geranium, honey essence, rose oil, vanilla, lemon oil, orange oil, cassia, caraway, cognac, jasmine, ylang-ylang, sage, fennel, piment, ginger, anise, coriander, coffee, or a mint oil from any species of the genus  Mentha ), flavour enhancers, bitterness receptor site blockers, sensorial receptor site activators or stimulators, sugars and/or sugar substitutes (e.g., sucralose, acesulfame potassium, aspartame, saccharine, cyclamates, lactose, sucrose, glucose, fructose, sorbitol, or mannitol), and other substances or additives such as charcoal, chlorophyll, minerals, botanicals, or breath freshening agents. They may be imitation, synthetic or natural ingredients or blends thereof. They may be in any suitable form, for example, oil, liquid, or powder. 
     In the figures described herein, like reference numerals are used to illustrate equivalent features, articles or components. 
       FIG. 1 a    is a side-on cross sectional view of a first filter unit  1  including a tube  2 , formed from filter material in the present example, and forming part of a smoking article  3 . The smoking article  3  has a mouth end  3   a , arranged to be placed in the user&#39;s mouth when smoking, and a lit end  3   b , arranged to be lit when smoking. The filter unit  1  is connected to an aerosol generating material  4 , in the present case cut tobacco in the form of a rod, by a tipping paper  5 . The aerosol generating material  4  is wrapped in a wrapper  6 , for instance cigarette paper. 
     The tube  2  comprises a wall having inner and outer surfaces which are substantially circular in cross section, in the present example, for cross sections taken along the longitudinal length of the tube. An inner diameter of the tube  2  is defined between two diametrically opposite points on the inner surface of the wall of the tube, while an outer diameter of the tube  2  is defined between two diametrically opposite points on the outer surface of the wall of the tube. The wall of the tube  2  may have a thickness in the range of about 0.5 mm to about 5 mm. For example, the wall may have a thickness of between about 1 mm and about 4 mm, between about 1.0 mm and about 3 mm or between about 1.0 mm and about 2 mm, or between about 1.5 mm and 2.5 mm, or about 1.3 mm. In a particular embodiment, the wall may have a thickness of about 2.2 mm, having an inner diameter of about 3.0 mm and an outer circumference of about 23.4 mm. Where the wall thickness varies along the length of the tube  2 , the thickness values set out above can be taken as the maximum thickness of the wall. 
     The tube  2  has a first portion  2   a  and a second portion  2   b . In  FIG. 1 , these portions  2   a ,  2   b  are disposed longitudinally along the length of the tube  2 . As shown in  FIG. 1 , the first and second portions  2   a ,  2   b  are arranged either side of a longitudinal position on the tube indicated by dashed line ‘X’. The first portion  2   a  of the tube  2  extends from an end of the tube  2  furthest from the mouth end  3   a  of the smoking article  3  up to the dashed line ‘X’, and the second portion  2   b  of the tube  2  extends from the dashed line ‘X’ to the mouth end  3   a  of the smoking article. An inner diameter of the first portion  2   a  of the tube  2  is different from an inner diameter of the second portion  2   b  of the tube  2 . The second portion  2   b  is at a distal end of the filter unit, in particular at the mouth end  3   a  of the smoking article  3  in the present example. 
     In the present example, an inner diameter of the second portion  2   b , illustrated in  FIG. 1 a    by arrow ‘B’, is greater than an inner diameter of the first portion  2   a , illustrated by arrow ‘A’. The inner diameter ‘A’ of the first portion  2   a  can be in the range of about 2 mm to about 6 mm, about 3 mm to about 5 mm, or about 3 mm to about 4 mm. For example, the inner diameter of the first portion  2   a  may be about 3 mm, about 4 mm or about 5 mm. The inner diameter ‘B’ of the second portion  2   b  varies along the length of the second portion  2   b  in the present example. The largest inner diameter ‘B’ of the second portion  2   b  can be in the range of about 2.5 mm to about 8 mm, about 3 mm to about 7 mm, or about 4 mm to about 6 mm. For example, the largest inner diameter ‘B’ of the second portion  2   b  may be about 5 mm. In a particular embodiment, the wall may have a thickness of about 2.2 mm in the first portion  2   a  and an inner diameter ‘A’ of the first portion of about 3 mm, and a largest internal diameter ‘B’ of the second portion  2   b  may be about 5.45 mm, while the tube  2  has an outer circumference of about 23.4 mm. In alternative examples, the circumference of the tube  2  can vary between about 20 mm and about 25 mm, for instance between about 22 mm and about 25 mm. The circumference of the tube  2  can be, for instance, about 24.8 mm, about 23.4 mm or greater than about 22 mm. 
     The overall length of the tube  2  may be in the range of about 3 mm to about 25 mm, or about 5 mm to about 12 mm. For example, the length of the tube  2  may be about 5, 6, 7, 8, 9 or 10 mm. 
     The length of the first portion  2   a  may be in the range of about 2 mm to about 25 mm, or about 4 mm to about 10 mm. For example, the length of the first portion  2   a  may be about 4, 5, 6, 7, 8 or 9 mm. 
     The length of the second portion  2   b  may be in the range of about 0.5 mm to 8 mm. For example, the length of the second portion  2   b  may be about 1 mm to about 5 mm, about 1 mm to about 3 mm, about 2 mm or about 1.2 mm. 
     The non-uniformity in inner diameter of the second portion  2   b  may be formed by indenting the filter material at the end of the tube  2  closest to the mouth end  3   a  of the smoking article. The tube  2  of filter material can have a first end surface at the end of the tube  2  at the mouth end  3   a  of the smoking article  3  and a second end surface at its longitudinal end opposite to the first end surface. In the present example, the first and second end surfaces are perpendicular to the longitudinal axis, although they could alternatively be at an angle other than 90° to the longitudinal axis. The tube  2  of filter material is formed from a plurality of continuous fibres extending between said first and second end surfaces. For instance, the filter material can be cellulose acetate tow with a denier per filament of between 3 dpf and 8 dpf and a total denier of between 15,000 and 40,000 denier. In one example, the filter material comprises a cellulose acetate tow with a denier per filament of 5 dpf and a total denier of 30,000 denier. In another example, the filter material comprises a cellulose acetate tow with a denier per filament of 7 dpf and a total denier of 36,000 or 33,000 denier. The filter material can comprise between 12% and 25% plasticiser by weight. For instance, filter material can comprise between about 15% and 21% plasticiser or from about 17% to 18% plasticiser by weight. The density of the filter material is greater at the first end surface than at said second end surface. This is, for instance, due to the indentation or other compression of the filter material to form the second portion  2   b  having reduced diameter. 
     The ‘in-product’ filter hardness of the filter units described herein refers to the filter rigidity when measured 3 mm from the mouth end of the filter unit in the final product, using a Borgwaldt H10 measurement device or similar apparatus. In-product hardness is defined as the ratio between the height h 0  of a filter segment and the remaining height h 1  having a defined load applied. It is stated as a percentage of the h 0  (and therefore has no physical unit of measure). 
     In-product hardness=(h 1 /h 0 )×100 
     Where, 
     h 0 =initial height 
     h 1 =remaining height (under load) 
     Samples are conditioned at 22° C./60% r.H. for a minimum of 48 hours. A total of 20 specimens are tested. 
     Instrument parameters are set to the following: 
     Lowering Speed: 0.6 mm/s 
     Load Weight: 150 g 
     Load Time: 5 s 
     Contact Time: 1 s 
     Contact Weight: 2 g 
     Lower load bar: plain 
     Upper load bar: R 3 mm 
     Upon use of the Borgwaldt H10 measurement device, the samples are placed in the hopper and testing is performed automatically such that each individual sample is measured for both h 0  and h 1  at a first measurement position under the load bar. The sample is then moved to the next measurement position and the heights will be measured again. The process repeats until all samples provided are measured at all measurement positions. 
     The hardness of the tubes described herein, as measured according to the above process and with the tube forming the mouth-end filter component of a cigarette, can be between about 85% and 95%, in particular between about 88% and 94% and in one example about 89%. The process of indenting the filter material to form the non-uniformity in inner diameter of the second portion  2   b  can increase the hardness of the tube by between about 2% and about 10%, between about 2% and about 6% or about 5% or about 6%. In one example of a tube having an inner diameter of 3 mm, an outer circumference of 23.4 mm, a tow specification of 5.0Y30,000 and a base rod hardness of 92% before application to a cigarette, the hardness has been measured as 84.7% when applied to a cigarette and 89.4% when a 45°, 1.2 mm depth chamfer is applied to the inner mouth-end edge of the tube. The tube segment is 7 mm in length, and has a segment weight (unwrapped) of 49 mg and 17% triacetin plasticiser. The tube is combined with first and second upstream filter segments (for instance a first segment comprising filter material and a 3.0 mm capsule as described herein embedded within a central portion of the filter material, and a second segment, upstream of the first segment, comprising particles of activated carbon dispersed within filter material). The overall filter length can be between about 15 mm and about 30 mm, for instance about 27 mm. 
     In another example of a tube having an inner diameter of 3 mm, an outer circumference of 23.4 mm, a tow specification of 7.0Y33,000 and a base rod hardness of 94% before application to a cigarette, the hardness has been measured as 87.9% when applied to a cigarette and 91.6% when a 45°, 1.2 mm depth chamfer is applied to the inner mouth-end edge of the tube. The tube segment is 7 mm in length, and has a segment weight (unwrapped) of 54 mg and 17% triacetin plasticiser. The tube is combined with first and second upstream filter segments as described above. 
     In another example of a tube having an inner diameter of 3 mm, an outer circumference of 23.4 mm, a tow specification of 7.0Y36,000 and a base rod hardness of 96% before application to a cigarette, the hardness has been measured as 91.2% when applied to a cigarette and 93.3% when a 45°, 1.2 mm depth chamfer is applied to the inner mouth-end edge of the tube. The tube segment is 7 mm in length, and has a segment weight (unwrapped) of 60 mg and 18% triacetin plasticiser. The tube is combined with first and second upstream filter segments as described above. 
     The tube tow weight can be in the range of 600 to 800 mg, for instance 700 mg to 730 mg for an 84 mm base rod length. 
     Table 1 below provides the hardness level for tubes before and after chamfering based on a 45°, 1.2 mm depth chamfer applied to the inner mouth-end edge of the tube. 50 samples for each of three starting tube designs were tested. The tubes had a circumference of 23.18 mm, a 7 mm length, an inner diameter of 3 mm, a wall thickness of 2.1 m, a 5Y30,000 cellulose acetate tow (49.16 mg) wrapped in a 27 gsm plug wrap and 17% triacetin plasticiser by weight of tow. The shaping head  42  used to form the chamfer (see further details provided below) was heated to 230° C. and spun at 250 rpm when contacted with the filter unit to form the recess. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Unchamfered Tube (hardness %) 
                 Chamfered Tube (hardness %) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Mean 
                 84.7 
                 87.9 
                 91.2 
                 89.4 
                 91.6 
                 93.3 
               
               
                 SD 
                 0.9 
                 0.8 
                 0.7 
                 0.9 
                 0.7 
                 0.6 
               
               
                 CofV 
                 1.10 
                 0.92 
                 0.79 
                 1.05 
                 0.77 
                 0.61 
               
               
                 Max 
                 87.1 
                 89.4 
                 92.6 
                 91.8 
                 92.9 
                 95.0 
               
               
                 Min 
                 82.6 
                 85.7 
                 89.8 
                 87.1 
                 90.1 
                 91.8 
               
               
                 Range 
                 4.5 
                 3.7 
                 2.8 
                 4.7 
                 2.8 
                 3.2 
               
               
                   
               
            
           
         
       
     
     Alternatively, the non-uniformity in inner diameter of the second portion  2   b  may be formed by cutting the end of the tube  2  to remove filter material from the end of the tube  2 . This can give rise to a reduction rather than an increase in tube hardness. 
     In the present example, as illustrated in  FIG. 1 a   . the outer diameter of the second portion  2   b  is the same as the outer diameter of the first portion  2   a.    
     In the present example, each of the first portion  2   a  and the second portion  2   b  has a first end and a second end. The second end of the first portion  2   a  adjoins the first end of the second portion  2   b , and has an inner diameter substantially the same as the first end of the second portion  2   b.    
     The tube  2  has a longitudinal axis (not shown). The inner surface of the first portion  2   a  is substantially parallel to the longitudinal axis of the tube  2 . The inner surface of the second portion  2   b  is chamfered in that it is at an angle to the longitudinal axis of the tube  2 , in the present example. The inner diameter of the second portion  2   b  decreases with distance from a distal end, for instance the mouth end  3   a , of the filter unit. The angle of intersection between a straight line following the inner surface of the second portion  2   b  of the tube  2  and the longitudinal axis of the tube  2  may be any angle other than 90°, for instance an angle in the range of about 10° to about 8°, or about 20° to about 70°, or about 30° to about 60°. For example, the angle may be about 45°. 
       FIG. 1 c    is a further side-on cross sectional view of the tube  2  formed from filter material of  FIG. 1 a   , illustrating the angle of intersection ‘θ’ between a straight line ‘Z’ following the inner surface of the second portion  2   b  of the tube  2  and the longitudinal axis ‘Y’ of the tube  2 . The angle of intersection ‘θ’ may be any angle other than 90°, for instance an angle in the range of about 10° to about 80°, or about 20° to about 70°, or about 30° to about 60°. For example, the angle may be about 45°. 
     Although a tube  2  having a uniformly chamfered inner edge has been described with reference to  FIGS. 1 a  and 1 c   , other tube shapes can be used. For instance, the second portion  2   b  of the tube  2  can have an inner diameter ‘B’ which is uniform along the length of the second portion  2   b , and therefore forms a step at the location shown by line ‘X’ between the first and second portions  2   a ,  2   b . Alternatively or in addition, a chamfer or step as described in respect of the inner diameter of the second portion  2   b  of the tube  2  may be provided in the outer diameter of the second portion  2   b  of the tube  2 . 
       FIG. 1 b    illustrates an outer chamfered tube  2 ′ which can be used in place of the tube  2  used in the smoking article  3  of  FIG. 1 a   , in which a chamfer is provided on an outer edge of the tube  2 ′ such that an outer diameter of the second portion  2   b ′, illustrated in  FIG. 1 b    by arrow ‘D’, is smaller than an outer diameter of the first portion  2   a ′, illustrated by arrow ‘C’.  FIG. 1 d    is a further side-on cross sectional view of the outer chamfered tube of  FIG. 1 b   . As shown in  FIG. 1 d   , the tube  2 ′ has a longitudinal axis ‘Y’. The outer surface of the first portion  2   a ′ is substantially parallel to the longitudinal axis ‘Y’ of the tube  2 ′. The outer surface of the second portion  2   b ′ is chamfered in that it is at an angle to the longitudinal axis of the tube  2 ′, in the present example. The angle of intersection ‘θ’ between a straight line ‘Z’ following the outer surface of the second portion  2   b ′ of the tube  2 ′ and the longitudinal axis ‘Y’ of the tube  2 ′ may be any angle other than 90°, for instance an angle in the range of about 10° to about 8°, or about 20° to about 70°, or about 30° to about 60°. For example, the angle may be about 45°. 
     In summary, tubes  2 ,  2 ′ are formed from filter material and have a longitudinal axis ‘Y’, wherein a straight line ‘Z’ following at least a portion of an internal or external surface of the tube  2 ,  2 ′ would intersect the longitudinal axis ‘Y’ at an angle other than 90°. The internal or external surface of the tube  2 ,  2 ′ is adjacent to a longitudinal end surface of the tube  2 ,  2 ′. 
     The straight line ‘Z’ can be taken as a first straight line following a first portion of the internal or external surface of the tube and a second straight line following a second portion of the internal or external surface of the tube can be parallel to the longitudinal axis ‘Y’. For instance, the internal and external surfaces of the first portion  2   a ,  2   a ′ of the tubes  2 ,  2 ′ of  FIGS. 1 a  and 1 b    extend at a fixed distance from said longitudinal axis and therefore straight lines following such surfaces would be parallel to the longitudinal axis. 
     The angle other than 90° can be between about 20° and about 70°, and/or between about 30° and about 60° and/or between about 35° and about 55° and/or is about 45°. 
     Referring again to  FIG. 1 a   , in the present example, the first filter unit  1  further includes a sleeve  7 . The sleeve  7  is formed from a sheet material such as plug wrap. In alternative examples, the sleeve  7  can be formed in other ways, for instance from plastic or other materials. 
     The first filter unit  1  also includes an upstream filter segment  8 , arranged upstream of the tube  2  in the direction of mainstream smoke when the smoking article is drawn on by a user. The upstream filter segment  8  has a longitudinal axis (not shown). The upstream filter segment  8  has a curved outer surface  8   a  circumscribing the segment  8 , a first longitudinal end surface  8   a  closest to the lit end  3   a  of the smoking article  3  and a second longitudinal end surface  8   b  closest to the mouth end  3   a  of the smoking article  3 . The longitudinal end surfaces  8   a ,  8   b  are perpendicular to the longitudinal axis of the upstream filter segment  8 . In the present example, the tube  2  and the upstream filter segment  8  have a common longitudinal axis. 
     The sleeve  7  is wrapped around the tube  2  and the upstream filter segment  8 . In the present example, an adhesive is provided between the sleeve  7  and the tube  2  and upstream filter segment  8  and in this way the sleeve  7  connects the tube  2  to the upstream filter segment  8 . 
     In the present example, the end of the tube  2  closest to the mouth end  3   a  of the smoking article  3  is flush with the end of the sleeve  7  closest to the mouth end  3   a  of the smoking article  3 . However, in alternative examples, the tube  2  may extend beyond the end of the sleeve  7  closest to the mouth end  3   a  of the smoking article  3 , or may stop short of the end of the sleeve  7  closest to the mouth end  3   a  of the smoking article  3 . For instance, when the outer chamfered tube  2 ′ of  FIG. 1 b    is used in place of the tube  2  of  FIG. 1 a   , the sleeve  7  may surround only the first portion  2   a ′ of the tube  2 ′, and the tipping  5  can also extend up to the edge of the sleeve  7  closest to the mouth end  3   a  of the smoking article  3 . In this way, the smoking article  3  can be provided with an outer chamfered edge at the mouth end  3   a  giving a smooth surface against which the users lips can be placed, facilitating the user in holding the smoking article in their mouth. In the present example, the sleeve  7  fully surrounds the outer surface of the upstream filter segment  8 . 
     The length of the upstream filter segment  8  may be selected according to the desired filtration performance of the filter unit  1 , and may be in the range 5 mm to 25 mm, or 10 mm to 15 mm. For example, the length of the upstream filter segment  8  may be about 12 mm. 
     The outer diameter of the upstream filter segment  8  may be substantially the same as the outer diameter of the tube  2 . Either or both of the tube  2  and the upstream filter segment may comprise a separate plug wrap (not shown) around which the sleeve  7  is wrapped. 
     The tube  2  and upstream filter segment  8  may be formed of filter material, in particular a fibrous filter material. The tube  2  and/or upstream filter segment  8  can contain substances such as additives or agents for modifying the aerosol, in the present case smoke, generated by the smoking article  3 . For example, a frangible capsule (not shown) containing a flavourant or other additive such as water may be located within the upstream filter segment  8 . The capsule can be located at a central longitudinal position within the upstream filter segment  8 , or may be offset from the central longitudinal position. 
     The capsule has a liquid centre and a frangible outer shell which can be broken by a user by squeezing the filter unit  1 , to thereby release the flavourant. The flavourant is transferred to the aerosol generated by the smoking article  3  as the smoking article  3  is smoked by the user. 
     In alternative examples, the first filter unit  1  may include alternative substances such as additives or agents for modifying the aerosol generated by the smoking article  3 , such as granules of activated carbon or other adsorbents, humectants, diluents etc. 
     The smoking article  3  can be a cigarette in any of the smoking article formats described herein. 
       FIG. 1 e    is a side-on cross sectional view of a filter insert  10  for use with the filter unit of  FIG. 1 a   . The filter insert  10  includes a cylindrical element  11  formed from cellulose acetate tow wrapped in a sleeve  12 , in the present case a plug wrap. The filter insert  10  may be inserted into the hollow centre of the tube  2  of the smoking article  3  by a user, for instance such that the insert  10  abuts the second longitudinal end surface  8   b  of the upstream filter segment  8 . The filter insert  10  may include a smoke modifying substance or additive allowing the user to alter properties of the aerosol passing through the smoking article  3  when the smoking article  3  is smoked and the filter insert  10  is inserted into the tube  2 . The inner chamfer in the second portion  2   b  of the tube  2  can facilitate insertion of the filter insert  10  into the tube  2  and, for instance, enable the outer diameter of the filter insert  10  to be substantially the same as the inner diameter ‘A’ of the tube  2 , which would otherwise make insertion of the insert  10  into the tube difficult. 
       FIG. 2  is a side-on cross sectional view of a discrete second filter unit  15  including a tube  16  formed from filter material and provided as a separate unit  15  for use with a smoking article  17 . The second filter unit  15  can be attached onto the mouth end  17   a  of the smoking article  17  by a user. The second filter unit  15  is configured to modify one or more properties of an aerosol, such as smoke, which is generated by the smoking article  17 . The second filter unit  15  has a mouth end  16   a  arranged to be inserted into a user&#39;s mouth when the second filter unit  15  is attached to the smoking article  17 . 
     The tube  16  of the second filter unit  15  is generally similar in design to the tube  2  of the first filter unit  1  illustrated in  FIG. 1 a   , and corresponding features and dimensions apply except where alternatively stated below. 
     The tube  16  has a first portion  16   a  and a second portion  15   b . These portions  16   a ,  16   b  are the portions of the tube  16  either side of a longitudinal position on the tube indicated in  FIG. 2  by dashed line ‘X’. The first portion  16   a  of the tube  16  extends from an end of the tube  16  closest to the mouth end  16   a  of the second filter unit  15  up to the dashed line ‘X’, and the second portion  16   b  of the tube  16  extends from the dashed line ‘X’ to the edge of the tube  16  furthest from the mouth end  16   a  of the filter unit. An inner diameter of the first portion  16   a  of the tube  16  is different from an inner diameter of the second portion  16   b  of the tube  16 . 
     In the present example, an inner diameter of the second portion  16   b , illustrated in  FIG. 2  by arrow ‘B’, is greater than an inner diameter of the first portion  16   a , illustrated by arrow ‘A’. The inner diameter ‘A’ of the first portion  16   a  may be in the range of about 5 mm to about 10 mm, about 6 mm to about 9 mm, or about 6 mm to about 9 mm. For example, the inner diameter of the first portion  16   a  may be about 8 mm. Inner diameter of the first portion may be selected to correspond to the outer diameter of the mouth end  17   a  of the smoking article  17 . The inner diameter ‘B’ of the second portion  16   b  varies along the length of the second portion  16   b  in the present example. The largest inner diameter ‘B’ of the second portion  16   b  can be in the range of about 6 mm to about 12 mm, about 6 mm to about 10 mm, or about 8 mm to about 10 mm. For example, the largest inner diameter ‘B’ of the second portion  2   b  may be about 9 mm. 
     In the present example, the outer diameter of the second portion  16   b  is the same as the outer diameter of the first portion  16   a.    
     In the present example, the second filter unit  15  further includes a sleeve  18 . The sleeve  18  is formed from a sheet material such as plug wrap. In alternative examples, the sleeve  18  can be formed in other ways, for instance from plastic or other materials. 
     The second filter unit  15  also includes a downstream filter segment  19 , arranged downstream of the tube  16  in the direction of mainstream smoke when the smoking article  17  is drawn on by a user with the second filter unit  15  attached to the smoking article  17 . The downstream filter segment  19  has a longitudinal axis (not shown). The downstream filter segment  19  has a longitudinal end surface  19   a  furthest from the mouth end  16   a  of the second filter unit  15 . In the present example, the tube  16  and the downstream filter segment  19  have a common longitudinal axis. 
     The sleeve  18  is wrapped around the tube  16  and the downstream filter segment  19 . In the present example, an adhesive is provided between the sleeve  18  and the tube  16  and downstream filter segment  19  and in this way the sleeve  18  connects the tube  16  to the downstream filter segment  19 . 
     In the present example, the end of the tube  16  furthest from the mouth end  16   a  of the second filter unit  15  extends beyond the end of the sleeve  18  furthest from the mouth end  16   a  of the second filter unit  15 . In the present example, the tube  16  extends 0.5 mm beyond the sleeve  18 . However, in alternative examples, the tube  16  may extend between about 0.5 and 10 mm, for instance between about 0.5 mm and 3 mm beyond the end of the sleeve  18  furthest from the mouth end  16   a  of the second filter unit  15 , or may be flush with the edge of the sleeve  18  or stop short of the end of the sleeve  18  furthest from the mouth end  16   a  of the filter element  15 . In the present example, the sleeve  18  fully surrounds the outer surface of the downstream filter segment  19 . 
     The length of the downstream filter segment  19  may be selected according to the desired filtration performance of the second filter unit  15 , and may be in the range 5 mm to 25 mm, or 10 mm to 15 mm. For example, the length of the downstream filter segment  19  may be about 12 mm. 
     The outer diameter of the downstream filter segment  19  may be substantially the same as the outer diameter of the tube  16 . Either or both of the tube  16  and the downstream filter segment  19  may comprise a separate plug wrap (not shown) around which the sleeve  18  is wrapped. 
     The tube  16  and downstream segment  19  may be formed of filter material, in particular a fibrous filter material, as described herein. The tube  16  and/or downstream segment  19  can contain substances such as additives or agents for modifying the aerosol, in the present case smoke, generated by the smoking article  17 . For example, a frangible capsule (not shown) as described elsewhere herein and containing a flavourant or other additive may be located within the downstream filter segment  19 . The capsule can be located at a central longitudinal position within the downstream filter segment  19 , or may be offset from the central longitudinal position. 
     In alternative examples, the second filter unit  15  may include alternative substances such as additives or agents for modifying the aerosol generated by the smoking article  17 , such as granules of activated carbon or other adsorbents, humectants, diluents etc. The smoking article  17  can be a conventional cigarette in any of the smoking article formats described herein. 
     The discrete second filter unit  15  can be coupled or attached to the smoking article  17  by a user. In the present example, the tube  16  of the second filter unit  15  is arranged to receive a mouth end portion  17   a  of the smoking article  17  so that the second filter unit  15  and the smoking article  17  can be attached or coupled together by a user. The mouth end  17   a  of the smoking article  17 , in the present example, abuts the longitudinal end surface  19   a  when the second filter unit  15  is connected to the smoking article  17 . The user can select whether or not to attach the second filter unit  15  to the smoking article  17  prior to smoking the smoking article  17 , and can in this way control the length of filter of the smoking article  17  and therefore the level of filtration of the aerosol generated by the smoking article  17 , as well as any other modification of the aerosol performed by the second filter unit  15 . 
     The second filter unit  15  may be attached to the smoking article  17  in any suitable way. This may include forming an interference fit between an inner surface of the tube  16  and an outer surface of the smoking article  17 . In this case, the interference fit is such that a seal is formed at the interface between the inner surface of the tube  16  and the outer surface of the smoking article  17 , which inhibits the ingress of gases (such as air) that would normally enter into the smoking article  17  via a gap between the outer surface of the smoking article  17  and the inner surface of the tube  16 . The amount of air entering into a smoking article between the two neighbouring surfaces may be variable and/or unwanted. Restricting the ingress of air therefore provides a degree of control of the airflow into and/or through the smoking article  17 . 
     The tube  16  has a longitudinal axis (not shown). The inner surface of the first portion  16   a  is substantially parallel to the longitudinal axis of the tube  16 . The inner surface of the second portion  16   b  is chamfered in that it is at an angle to the longitudinal axis of the tube  16 , in the present example. The angle of intersection between a straight line following the inner surface of the second portion  16   b  of the tube  16  and the longitudinal axis of the tube  16  may be in the range of about 10° to about 8°, or about 20° to about 70°, or about 30° to about 60°. For example, the angle may be about 45°. 
     In the present example, the inner portion of the edge of the tube  16  furthest from the mouth end  16   a  of the second filter unit  16  is chamfered such that an inner diameter of the second portion  16   b , illustrated by arrow ‘B’ is greater than an inner diameter of the first portion  16   a , illustrated by arrow ‘A’. This arrangement makes it easier for the user to insert an end  17   a  of the smoking article  17  into the tube  16 , in order to couple the second filter unit  15  to the smoking article  17 . 
       FIG. 3 a    is a side-on cross sectional view of a third filter unit  20  forming part of a smoking article  21 . The third filter unit  20  comprises a body  22  formed of filter material. The smoking article  21  includes a rod of aerosol generating material  23 , in the present case cut tobacco, wrapped in a sheet material  24 , in the present case cigarette paper. The rod  23  and third filter unit  20  are connected by tipping  25 , which surrounds the third filter unit  20  and partially surrounds the rod  23 . The smoking article  21  has a mouth end  21   a  to be inserted in the user&#39;s mouth when smoking. The body  22  of the third filter unit  20  has an end surface  26  at the end of the body  22  closest to the mouth end  21   a  of the smoking article  21  furthest from the rod  23  and a recess  27  formed in the end surface  26 . The recess  27  is a hollow depression in the body  22 . The recess  27  extends into, but not entirely through, the body  22 . In the present example, the body  22  is cylindrical, and the end surface  26  is a longitudinal end surface of the body  22 . 
     In the present example, the recess  27  has the shape of a conical frustum, and has an inner base surface  27   a  and an inner side surface  27   b . In other examples, the recess  27  may have the shape of other frustums, and may have multiple side surfaces. Alternatively, the recess may be cylindrical, conical or hemispherical in shape. 
     The recess  27  may be formed in the filter material of the body  22  by indentation. In this case, the filter material of the body  22  may be compressed during formation of the recess  27 . In other words, the filter material at or close to an inner surface of the recess  27 , for instance at a first longitudinal end surface  26  of the body  22 , is denser than the filter material in other areas of the body  22 , such as the end of the body  22 , or second longitudinal end surface of the body  22  furthest from the first longitudinal end surface  26 . Alternatively, the recess  27  can be formed by removing filter material from the body  22  at the end surface  26 . The recess  27  can direct smoke to a particular portion of the body  22  in which the recess  27  is located, by reducing the volume of material in that part of the body  22 , and enable particular formations of smoke from the mouth end  21   a  of the smoking article  21 . The formation of the recess  27  can result in a net increase or decrease in the resistance to draw of the body  22  of filter material. In this way, the formation of the recess  27  can be used to adjust the resistance to draw of the body  22  of filter material after the body  22  has been formed. The shape of the recess  27  may influence whether it increases or decreases the resistance to draw, with deeper, narrower recesses being more likely to reduce the resistance to draw than shallower, wider recesses. The resistance to draw may be altered by at least 5 mmWG by the formation of the recess  27 , or by at least 6, 7, 8 or 9 mmWG. In the examples of the recess provided herein, the recess can be arranged to alter the resistance to draw by at least 10 mmWG. In the examples of the recess provided herein, the recess can be arranged to reduce the resistance to draw by at least 5 mmWG, or at least 10 mmWG. 
     The body  22  may include a smoke modifying substance or additive (not shown) disposed within the filter material of the body  22 . The smoke modifying substance or additive may be any smoke modifying additive, such as flavours or other additives, as described herein. 
     The third filter unit  20  may further include a sleeve  28 , such as plug wrap, which is wrapped around the body  22 . In the present example, the body  22  is flush at the mouth end  21   a  of the smoking article with the edge of the sleeve  28 . In other examples, the sleeve  28  and/or tipping  25  may extend beyond an end of the body  22 . The space thus formed by the sleeve  28  and/or tipping  25  extending beyond an end of the body  22 , such as the longitudinal end surface  26 , may be arranged to receive a filter insert, such as that illustrated in  FIG. 1   e.    
       FIG. 3 b    is an end-on view of the third filter unit  20 . 
       FIG. 3 c    is an end-on view of another design for a third filter unit  20   i , in this case having a triangular shaped recess having an inner base surface  27   a ′ and inner side surfaces  27   b ′ and longitudinal end surface  26 ′. 
       FIG. 3 d    is an end-on view of another design for a third filter unit  20   ii , in this case having a hexagonal shaped recess having an inner base surface  27   a ″ and inner side surfaces  27   b ″ and longitudinal end surface  26 ″. 
       FIG. 3 e    is an end-on view of another design for a third filter unit  20   iii , this design having a substantially cone shaped recess  27   iii .  FIG. 3 e   ′ is a side-on cross sectional view of the third filter unit  20   iii  of  FIG. 3 e   . The recess  27   iii  of  FIG. 3 e    extends substantially across the whole end surface of the body  22   iii . The cone shape of the recess  27   iii  is formed from a first conical frustum extending from the end surface approximately two thirds of the depth of the recess and then capped by a second cone having a steeper slant than the first conical frustum extending for the final third of the depth into the body  22   iii . The slant angle of the first conical frustum can be between 30° and 60°, in the present case about 45°, with respect to the longitudinal axis of the cone. The slant angle of the second cone can be between 20° and 40° from the longitudinal axis of the cone, in the present case about 30°. The body  22   iii  of filter material has reflective symmetry about the line ‘X’ which is perpendicular to the longitudinal axis of the body  22  and infinite rotational symmetry about the longitudinal axis. 
       FIG. 3 f    is an end-on view of another design for a third filter unit  20   iv , this design having a recess  27   iv  having a first portion in the form of a frustum cone, a second portion in the form of a cylinder and a third portion in the form of a cone.  FIG. 3 f    is a side-on cross sectional view of the third filter unit  20   iv  of  FIG. 3 f   . The first portion can extend a depth of approximately two fifths of the depth of the recess  27   iv  and have a slant angle of between 30° and 60° from the longitudinal axis of the cone, in the present case about 45°. The second portion in the form of a cylinder has a depth of approximately two fifths of the depth of the recess  27   iv  and a diameter of about 50% of the diameter of the filter unit  20   iv , centred on the longitudinal axis. The third portion in the form of a cone has a depth of approximately one fifth of the depth of the recess  27   iv  and a slant angle of between 45° and 75° from the longitudinal axis of the cone, in the present case about 60°. The body  22   iv  of filter material has reflective symmetry about the line ‘X’ which is perpendicular to the longitudinal axis of the body  22   iv  and infinite rotational symmetry about the longitudinal axis. 
       FIG. 3 g    is an end-on view of another design for a third filter unit  20   v , this design having a recess  27   v  having a first portion in the form of a cylinder and a second portion in the form of a cone.  FIG. 3 g   ′ is a side-on cross sectional view of the third filter unit  20   v  of  FIG. 3 g   . The first portion in the form of a cylinder has a depth of approximately three fifths of the depth of the recess  27   v  and a diameter of about 70% of the diameter of the filter unit  20   v , centred on the longitudinal axis. The second portion in the form of a cone has a depth of approximately two fifths of the depth of the recess  27   v  and a slant angle of between 30° and 60° from the longitudinal axis of the cone, in the present case about 45°. The body  22   v  of filter material has reflective symmetry about the line ‘X’ which is perpendicular to the longitudinal axis of the body  22   v  and infinite rotational symmetry about the longitudinal axis. 
       FIG. 3 h    is an end-on view of another design for a third filter unit  20   vi , this design having a recess  27   vi  in the form of a rhomboid prism.  FIG. 3 h   ′ is a side-on cross sectional view of the third filter unit  20   vi  of  FIG. 3 h   . The body  22   vi  of filter material has no lines of reflective symmetry. For instance, there is no reflective symmetry about any lines ‘X’ perpendicular to the longitudinal axis of the body  22   vi . The body  22   vi  has order 2 rotational symmetry about the longitudinal axis, in that a rotation of 180° about the longitudinal axis maps the body  22   vi  back onto itself. 
       FIG. 3 i    is an end-on view of another design for a third filter unit  20   vii , this design having a recess  27   vii  in the form of the capital letter ‘L’.  FIG. 3 i   ′ is a side-on cross sectional view of the third filter unit  20   vii  of  FIG. 3 i   . The body  22   vii  of filter material has no lines of reflective symmetry. For instance, there is no reflective symmetry about any lines ‘X’ perpendicular to the longitudinal axis of the body  22   vii . The body  22   vii  has order 1 rotational symmetry, or no rotational symmetry, about the longitudinal axis, in that only a rotation of 360° about the longitudinal axis maps the body  22   vii  back onto itself. 
       FIG. 3 j    is an end-on view of another design for a third filter unit  20   viii , this design having a recess  27   viii  in the form of the capital letter ‘Y’.  FIG. 3 j   ′ is a side-on cross sectional view of the third filter unit  20   viii  of  FIG. 3 j   . The body  22   viii  of filter material has no lines of reflective symmetry. For instance, there is no reflective symmetry about any lines ‘X’ perpendicular to the longitudinal axis of the body  22   viii . The body  22   viii  has order 1 rotational symmetry, or no rotational symmetry, about the longitudinal axis, in that only a rotation of 360° about the longitudinal axis maps the body  22   viii  back onto itself. 
     The third filter units  20  and  20   i  to  viii  described herein having a recess formed in an end surface can be used to form components of other filter units and filter inserts described herein. For instance, the third filter units  20  and  20   i  to  viii  described herein having a recess formed in an end surface can be used as the upstream filter segment  8  of the first filter unit  1  described with reference to  FIG. 1 a   , as the filter insert  10  as described with reference to  FIG. 1 e   , or as the downstream filter segment  19  of the second filter unit  15  described with reference to  FIG. 2 . In each case, the recess would be arranged to face the mouth end of the product. 
     The hardness of the third filter units  20  and  20   i  to  viii  described herein having a recess formed in an end surface, as measured according to the above process and with the filter unit forming the mouth-end filter component of a cigarette, can be between about 80% and 92%, in particular between about 82% and 88% and in some examples about 82%, 85% or 88%. The process of indenting the filter material to form the recess can increase the hardness of the filter by between about 2% and about 10% depending on the shape of the recess and the properties of the filter, between about 2% and about 6% or about 2%, about 5% or about 6%. 
     Table 2 below provides hardness level data for mono filters before and after they have been processed to form recesses as described with reference to  FIGS. 3 e , 3 f  and 3 g   . 50 samples for each filter unit were tested. The filters included a 3Y30,000 cellulose acetate tow with 8% triacetin plasticiser, had a circumference of 23.4 mm and were wrapped in a 27 gsm plug wrap. The shaping head  42  used to form the recesses (see further details provided below) was heated to 230° C. and spun at 250 rpm when contacted with the filter unit to form the recess. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 Filter Unit 
                 Filter Unit 
                 Filter Unit 
               
               
                 Hardness % 
                 Pre-Shaping 
                 20iii 
                 20iv 
                 20v 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Mean 
                 82.6 
                 84.7 
                 82.1 
                 87.9 
               
               
                 SD 
                 1.1 
                 1.1 
                 1.1 
                 1.0 
               
               
                 CofV 
                 1.37 
                 1.28 
                 1.38 
                 1.19 
               
               
                 Max 
                 85.3 
                 87.8 
                 83.8 
                 89.7 
               
               
                 Min 
                 79.8 
                 82.7 
                 79.5 
                 85.4 
               
               
                 Range 
                 5.5 
                 5.1 
                 4.3 
                 4.3 
               
               
                   
               
            
           
         
       
     
     Although described has having a single recess formed in an end surface thereof, the filter units can be provided with more than one recess. For instance, the end surface can be provided with between two and twelve separate recesses, either formed simultaneously or in separate process steps. Alternatively or in addition, a recess in the end surface can include portions having different depths into the end surface. The maximum depth of any of the recesses described herein can be between about 1 mm and about 12 mm, for instance between about 2 mm and about 10 mm or between about 2 mm and about 6 mm. The maximum width of any of the recesses described herein can be between about 1 mm and about 8 mm, for instance between about 2 mm and about 6 mm or between about 3 mm and about 5 mm. 
       FIG. 4  is a side-on cross sectional view of a fourth filter unit  30 , including a tube  31  formed from sheet material, and provided as a discrete component for use with a separate smoking article  17  as described with reference to  FIG. 2 . The fourth filter unit  30  has a mouth end  30   a  and comprises a tube  31  having a first portion  31   a  and a second portion  31   b . An inner diameter of the first portion  31   a  is different from an inner diameter of the second portion  31   b . The fourth filter unit  30  also includes a downstream filter plug  32  arranged closer to the mouth end  30   a  of the filter unit  30  than the tube  31  and formed from filter material. The fourth filter unit  30  further comprises a sleeve  33  partially surrounding the tube  31  and surrounding the downstream filter plug  32 . The tube  31  of the present example can be formed from a sheet material such as paper, card, cardboard, plastic or similar materials. 
     The fourth filter unit  30  can be coupled or attached to another tobacco industry product, such as smoking article  17 , by a user. The tube  31  is arranged to receive a portion of the smoking article  17 , for instance the mouth end  17   a  of the smoking article  17 , so that the filter unit  30  and the smoking article  17  can be attached or coupled together by a user. The fourth filter unit  30  is configured to modify one or more properties of an aerosol, such as smoke, which is generated by the smoking article  17 . 
     In the present example, the tube  31  is formed from a sheet material separate from the sleeve  33 , enabling the tube  31  to be formed of stiffer material than may be possible for use in wrapping the downstream filter plug  32 . An inner diameter ‘B’ of the second portion  31   b  is greater than an inner diameter ‘A’ of the first portion  31   a . This arrangement makes it easier for the user to couple the fourth filter unit  30  to the smoking article  17 . In the present example, an outer diameter ‘B’ of the second portion  31   b  is greater than an outer diameter of the first portion  31   a . This arrangement may be referred to as the tube  31  having a ‘widened end’. The dimensions of the tube  31  of  FIG. 4  can correspond to the dimensions of the tube  16  described with reference to  FIG. 2 . 
     The tube  31  formed from sheet material described with reference to  FIG. 4  can be used in place of the tube  2  at the mouth end of the smoking article  3  described with reference to  FIG. 1   a.    
       FIGS. 5 a  to 5 d    are perspective views of an apparatus  40  for shaping a tobacco industry product  41 . The tobacco industry product  41  may be (for example) a smoking article, a filter, or a tube, or other components described herein. The filter may be an individual filter unit, or may be part of a smoking article. The tube may be part of another tobacco industry product, e.g. a filter unit or a smoking article. Any of these tobacco industry products  41  may have a longitudinal axis. Any of these tobacco industry products may have a longitudinal end surface. Tubular components may also have an inner surface around the inside of the tube. The apparatus  40  can be used, for instance, to form any of the tubes  2 ,  2 ′,  16 ,  31  of the first, second and fourth filter units  1 ,  15 ,  30  described herein, or the recess  27  formed in the filter body  22  of the third filter unit  20  described herein. 
     Referring to  FIG. 5 a   , the apparatus  40  comprises a shaping head  42  configured to change the shape of a first end of the tobacco industry product  41  (not shown in this FIGURE). The apparatus  40  further comprises an actuator arrangement  43  configured to move the shaping head  42  and/or tobacco industry product  41 . The actuator arrangement  43  is configured to move the shaping head  42  and/or tobacco industry product  41  in a direction substantially parallel to a longitudinal axis of the tobacco industry product  41  such that the shaping head  42  is brought into contact with a first end  41   a  of the tobacco industry product  42  in order to change the shape of the first end  41   a.    
     Alternatively or in addition to the above, the actuator arrangement  43  can be configured to move the shaping head  42  and/or tobacco industry product  41  such that the shaping head  42  is brought into contact with a first longitudinal end surface and/or an inner surface of the tobacco industry product  42  in order to change the shape of the first longitudinal end surface and/or an inner surface. 
     In some examples, a receiving unit is arranged to receive and grip the tobacco industry product  41 , so as to hold tobacco industry product  41  in position while it is shaped. This may be achieved by mechanical means, such as a clamp, or alternatively by means such as vacuum suction, as described in more detail below. 
     In use, when the shaping head  42  is brought into contact with the first end  41   a  of the tobacco industry product  41 , the pressure exerted on the end  41   a  of the tobacco industry product  41  by the shaping head  42  deforms the material of the tobacco industry product  41 , thereby changing a shape of the end of the tobacco industry product  41 . Changing the shape of the end of the tobacco industry product  41  may, for instance, include changing an inner and/or outer diameter of the tobacco industry product  41 , as well as forming an indentation in the end  41   a.    
     The actuator arrangement  43  may be configured to move the shaping head  42  and/or tobacco industry product  41  in a reciprocating fashion. In other words, actuator arrangement  43  may be configured to move the shaping head  42  and/or tobacco industry product  41  so that they are first brought into contact with each other and are then moved apart from each other. 
     The shaping head  42  may be cylindrical in shape. In the present example, the shaping head  42  is substantially cylindrical in shape, and the end of the shaping head  42  has a chamfered profile. In other words, the shaping head  42  comprises a surface which is angled with respect to a side surface and a longitudinal end surface thereof. 
     In other exemplary arrangements, the shaping head  42  may be conical in shape. The shaping head  42  may have the shape of a frustum, such as a conical frustum. The shaping head  42  may be hemispherical in shape or may have a shape which has relatively low orders of rotational symmetry or no rotational symmetry. For instance, when forming the third filter units  20 ′ and  20 ″ of  FIGS. 3 c  and 3 d    herein, the end of the shaping head  42  would have a triangular frustum shape with order 3 rotational symmetry or a hexagonal frustum shape with order 6 rotational symmetry. The shaping head  42  can have, for instance, order 1 (also referred to herein as having no rotational symmetry), 2, 3, 4, 5, 6, 7, 8 or infinite/continuous rotational symmetry. 
     In the present example, the shaping head  42  has a longitudinal axis (not shown). The apparatus  40  is configured to rotate the shaping head  42  about its longitudinal axis, for instance for shaping heads  42  having infinite/continuous rotational symmetry. Rotating the shaping head  42  when the shaping head  42  is brought into contact with the end of the tobacco industry product  41  can provide a more even change in the shape of the end of the tobacco industry product  41 , resulting in a uniform end profile, compared to a fixed shaping head  42 . However, the apparatus  40  can be configured such that the shaping head  42  is fixed when the shaping head  42  has a relatively low order of symmetry, for instance order 1, 2, 3, 4, 5, 6, 7, 8 rotational symmetry. A known method of applying a shape to a filter which is visible from the mouth end of the filter is to create a tube filter having that shape running through the centre as a bore. However, in such cases, the standard cigarette making process requires such a shape to have at least order 2 rotational symmetry, otherwise the shape will not be the same when the tube is used in different orientations. The use of a shaping head  42  which can be applied directly to a filter body addresses this issue, meaning that shapes with order 1 rotational symmetry can be applied uniformly to cigarette filters. 
     The shaping heads described herein can be formed from a material such as metal, for instance stainless steel. The material can have a low coefficient of friction (i.e. non-stick) property or have a coating having a low coefficient of friction. The coefficient of friction of the material forming the body and/or coating of the shaping head can be less than 0.2 or less than 0.1. The material forming the body and/or coating of the shaping head can be thermally stable to at least 350° C. The material forming the body and/or coating of the shaping head can be capable of being heated via induction, as described further below. 
       FIGS. 6 a  to 6 i    are side-on views of respective first to ninth shaping heads  42 ,  42   i  to  42   viii  for use with the apparatus of  FIGS. 5 a  to 5 d   , the side on views being from the direction of the respective arrows of  FIGS. 6 a   ′ to  6   i ′, which are end-on views of the respective first to ninth shaping heads  42 ,  42   i  to  42   viii  of  FIGS. 6 a    to  6   i.    
     The first shaping head  42 , illustrated in  FIGS. 6 a  and 6 a   ′, comprises a conical frustum shape, and can be used to form the third filter unit  20  of  FIGS. 3 a  and 3 b   . The first shaping head  42  is arranged to be spinning when brought into contact with a body of filter material to form a recess. The second shaping head  42   i , illustrated in  FIGS. 6 b  and 6 b   ′, comprises a three-sided pyramidal frustum shape, and can be used to form the third filter unit  20   i  of  FIG. 3 c   . The second shaping head  42   i  is arranged to be in a fixed rotational position when brought into contact with a body of filter material to form a recess. The third shaping head  42   ii , illustrated in  FIGS. 6 c  and 6 c   ′, comprises a hexagonal based pyramidal frustum shape, and can be used to form the third filter unit  20   ii  of  FIG. 3 d   . The third shaping head  42   ii  is arranged to be in a fixed rotational position when brought into contact with a body of filter material to form a recess. 
     The fourth shaping head  42   iii , illustrated in  FIGS. 6 d  and 6 d   ′, is substantially cone shaped, and corresponds to the shape of and can be used to form the recess  27   iii  described with reference to  FIGS. 3 e  and 3 e   ′. The fourth shaping head  42   iii  has reflective symmetry about any line which is perpendicular to its longitudinal axis and infinite rotational symmetry about the longitudinal axis. The fourth shaping head  42   iii  is arranged to be spinning when brought into contact with a body of filter material to form a recess. 
     The fifth shaping head  42   iv , illustrated in  FIGS. 6 e  and 6 e   ′, corresponds to the shape of and can be used to form the recess  27   iv  described with reference to  FIGS. 3 f  and 3 f   . The fifth shaping head  42   iv  has reflective symmetry about any line which is perpendicular to its longitudinal axis and infinite rotational symmetry about the longitudinal axis. The fifth shaping head  42   iv  is arranged to be spinning when brought into contact with a body of filter material to form a recess. 
     The sixth shaping head  42   v , illustrated in  FIGS. 6 f  and 6 f   , corresponds to the shape of and can be used to form the recess  27   v  described with reference to  FIGS. 3 g  and 3 g   ′. The sixth shaping head  42   v  has reflective symmetry about any line which is perpendicular to its longitudinal axis and infinite rotational symmetry about the longitudinal axis. The sixth shaping head  42   v  is arranged to be spinning when brought into contact with a body of filter material to form a recess. 
     The seventh shaping head  42   vi , illustrated in  FIGS. 6 g  and 6 g   ′, corresponds to the shape of and can be used to form the recess  27   vi  described with reference to  FIGS. 3 h  and 3 h   ′. The seventh shaping head  42   vi  has no lines of reflective symmetry and order 2 rotational symmetry about the longitudinal axis of the shaping head  42   vi . The seventh shaping head  42   vi  is arranged to be in a fixed rotational position when brought into contact with a body of filter material to form a recess. 
     The eighth shaping head  42   vii , illustrated in  FIGS. 6 h  and 6 h   ′, corresponds to the shape of and can be used to form the recess  27   vii  described with reference to  FIGS. 3 i  and 3 i   ′. The eighth shaping head  42   vii  has no lines of reflective symmetry and order 1 rotational symmetry about the longitudinal axis of the shaping head  42   vii . The eighth shaping head  42   vii  is arranged to be in a fixed rotational position when brought into contact with a body of filter material to form a recess. 
     The ninth shaping head  42   viii , illustrated in  FIGS. 6 i  and 6 i   ′, corresponds to the shape of and can be used to form the recess  27   viii  described with reference to  FIGS. 3 j  and 3 j   ′. The ninth shaping head  42   viii  has no lines of reflective symmetry and order 1 rotational symmetry about the longitudinal axis of the shaping head  42   viii . The ninth shaping head  42   viii  is arranged to be in a fixed rotational position when brought into contact with a body of filter material to form a recess. 
     The apparatus  40  may be configured so that, in use, the longitudinal axis of the shaping head  42  and the longitudinal axis of the tobacco industry product  41  are aligned. In such an arrangement, the shaping head  42  and the tobacco industry product  41  may be said to have a common longitudinal axis. 
     In the present example, the apparatus  40  comprises a drum  43  arranged to move the tobacco industry product  41  relative to the shaping head  42  in order to bring the shaping head  42  into contact with an end of the tobacco industry product  41 . 
     The drum  43 , in the present example, is provided as a modification to the known separator drum used in cigarette manufacture to separate first and second tobacco rods so that a filter can be placed between the tobacco rods and the rods and filter can then be wrapped in tipping paper. The drum  43  is modified to include a head support unit  44  which supports a plurality of shaping heads  42  arranged such that they are spaced circumferentially around the drum  43 . The longitudinal axis of each of the shaping heads  42  is parallel to the axis of rotation of the drum  43 . The drum  43  includes a plurality of moving plates  45  in each of which first and second product receiving units or regions  46  are provided, in the form of flutes  46  in the present example. Each flute  46  is arranged to receive a tobacco industry product  41  and is generally shaped as an elongate groove formed in the plate  45  within which the tobacco industry product  41  can sit. The tobacco industry products  41  are held within the flutes  46  by suction through apertures formed in the base of the flutes  46 , as known in conventional separator and similar drums. 
     In the present example, the moving plates  45  move in a reciprocating manner towards and away from the shaping heads  42  held by the head support member  44  in order to bring tobacco industry products  41  into contact with the shaping heads  42 . In an alternative exemplary arrangement, the apparatus  40  may be configured so that both the plates  45  and the head support unit  44  are arranged to move in use, or so that only the head support unit  44  moves, in order to bring the shaping heads  42  into contact with the end of the tobacco industry product  41 . Should additional force be required to hold the tobacco industry products  41  within the product receiving regions  46  provided in the plates  45 , then these can be adapted to include an alternative gripping arrangement. Alternatively or additionally, a swash-plate type arrangement can be used to push tobacco industry products  41  longitudinally from the end opposite to the end which is to be shaped. 
     The apparatus  41  may further comprise a heating element  47  which is arranged to heat the shaping heads  42 . When the shaping heads  42  are heated during contact with the end of the tobacco industry product  41 , the heat may deform the material of the tobacco industry product  41 , which aids in changing the shape of the end of the tobacco industry product  41 . The heating element may be an induction coil. Alternatively, the shaping head  42  may be heated by a hot air system or a direct thermocouple. The shaping head can be heated to between 270° C. and 320° C., with a preferred temperature of 295° C. 
     As shown in  FIG. 5 d   , a gearing mechanism  48  can be used to rotate the shaping heads  42 , in the form of mandrels in the present example. Each mandrel  42  extends into a base shaft  42   a  which extends into and is supported by the head support unit  44 . In particular, the head support unit  44  includes first and second bearings  44   a ,  44   b  which support the base shaft  42   a  of each mandrel  42 , allowing it to rotate. Each mandrel base shaft  42   a  is also connected to and arranged to be turned via a mandrel driving cog  48   a  which in turn meshes with a fixed cog  48   b  extending around the periphery of the drum  43  and fixed in relation to the head support unit  44 . As the outer portions of the drum  43  rotate, including the head support unit  44 , this causes the mandrel driving cog  48   a  for each mandrel  42  to rotate as its teeth mesh with the fixed cog  48   b , and this rotates the mandrel  42 . Other arrangements for turning the shaping heads  42  can also be used, such as a separate motor arrangement for rotating one or more of the heads  42 . The mandrel driving cogs  48   a  can be removed from the mandrel base shafts  42   a  of the mandrels  42  in order to provide fixed rather than rotating mandrels  42 . 
     In an alternative exemplary arrangement, the apparatus  40  may further comprise a second shaping head (not shown) which is substantially the same as the shaping head  42  described above, and is arranged to change the shape of a second end of the tobacco industry product  41 . In this arrangement, the apparatus  40  can shape both ends of the tobacco industry product  900 , either simultaneously or in sequence. 
     Also presented herein is a method of shaping a tobacco industry product. The method is shown in  FIG. 7  and comprises the steps of: providing a tobacco industry product (S 101 ); and changing the shape of a first end of the tobacco industry product by moving a shaping head and/or the tobacco industry product in a direction substantially parallel to a longitudinal axis of the tobacco industry product such that the shaping head is brought into contact with the first end of the tobacco industry product (S 102 ). 
     Also presented herein is a further method of shaping a tobacco industry product. The method is shown in  FIG. 8  and comprises the steps of: providing the tobacco industry product (S 201 ); and changing the shape of a first end of the tobacco industry product by moving a shaping head and/or the tobacco industry product such that the shaping head is brought into contact with a first longitudinal end surface and/or an inner surface of the tobacco industry product (S 202 ). 
     In order to address various issues and advance the art, the entirety of this disclosure shows by way of illustration various embodiments in which the claimed invention(s) may be practiced and provide for superior smoking articles and filter units therefor. The advantages and features of the disclosure are of a representative sample of embodiments only, and are not exhaustive and/or exclusive. They are presented only to assist in understanding and teach the claimed features. It is to be understood that advantages, embodiments, examples, functions, features, structures, and/or other aspects of the disclosure are not to be considered limitations on the disclosure as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the scope and/or spirit of the disclosure. Various embodiments may suitably comprise, consist of, or consist essentially of, various combinations of the disclosed elements, components, features, parts, steps, means, etc. In addition, the disclosure includes other inventions not presently claimed, but which may be claimed in future.