Patent Publication Number: US-11039642-B2

Title: Smoking article with front-plug and aerosol-forming substrate and method

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a national phase application based on PCT/EP2012/077091, filed on Dec. 28, 2012. 
     The present specification relates to a smoking article comprising an aerosol-forming substrate for generating an inhalable aerosol when heated by a heating element. The specification also relates to a method of using such a smoking article. 
     Smoking articles in which an aerosol-forming substrate, such as a tobacco containing substrate, is heated rather than combusted are known in the art. The aim of such heated smoking articles is to reduce known harmful smoke constituents produced by the combustion and pyrolytic degradation of tobacco in conventional cigarettes. Typically in such heated smoking articles, an aerosol is generated by the transfer of heat from a heat source to a physically separate aerosol-forming substrate or material, which may be located within, around or downstream of the heat source. During smoking, volatile compounds are released from the aerosol-forming substrate by heat transfer from the heat source and entrained in air drawn through the smoking article. As the released compounds cool, they condense to form an aerosol that is inhaled by the consumer. 
     A number of prior art documents disclose aerosol-generating devices for consuming or smoking heated smoking articles. Such devices include, for example, heated smoking systems and electrically heated smoking systems. One advantage of these systems is that they significantly reduce sidestream smoke, while permitting the smoker to selectively suspend and reinitiate smoking. An example of a heated smoking system is disclosed in U.S. Pat. No. 5,144,962, which includes in one embodiment a flavour-generating medium in contact with a heater. When the flavour-generating medium is exhausted, both the flavour-generating medium and the heater are replaced. An aerosol-generating device where a smoking article can be replaced without the need to remove the heating element is desirable. 
     Typically, smoking articles for use with aerosol-generating devices comprise an aerosol-forming substrate that is assembled, often with other elements or components, in the form of a rod. Typically, such a rod is configured in shape and size to be inserted into an aerosol-generating device that comprises a heating element for heating the aerosol-forming substrate. 
     Direct contact between a heating element, for example an electrically actuated heating element, and the aerosol-forming substrate may provide an efficient means for heating the aerosol-forming substrate to form an inhalable aerosol. In such a device configuration, heat from a heating element may be conveyed almost instantaneously to at least a portion of the aerosol-forming substrate when the heating element is actuated, and this may facilitate the rapid generation of an aerosol. Furthermore, the overall heating energy required to generate an aerosol may be lower than would be the case in a system where the aerosol-forming substrate does not directly contact a heating element and initial heating of the aerosol-forming substrate occurs by convection or radiation. Where a heating element is in direct contact with an aerosol-forming substrate, the initial heating of portions of the aerosol-forming substrate that are in contact with the heating element will be effected by conduction. 
     Direct contact between a heating element and an aerosol-forming substrate may result in shrinkage of the aerosol-forming substrate. Shrinkage of the aerosol-forming substrate due to thermal contractions may cause the aerosol-forming substrate to adhere to a heating element. This may make it difficult to remove the smoking article from the heating element. The problems of adherence between a heating element and an aerosol-forming substrate may be particularly pronounced when the aerosol-forming substrate is in the form of a gathered sheet of homogenised tobacco material. Heating of such a substrate may be achieved by insertion of a heating element into the folds of the gathered sheet material. Shrinkage of such a substrate during heating may then cause the substrate to grip the heating element tightly, making it difficult to cleanly remove the heating element from the heating element. 
     Shrinkage of the aerosol-forming substrate may also loosen the aerosol-forming substrate within the smoking article. A preferred embodiment of a smoking article may be formed from a number of cylindrical elements arranged in sequence and assembled by wrapping with a cigarette paper. The cigarette paper preferably retains the elements in position by an interference interaction. Within the smoking article, the aerosol-forming substrate, or a cylindrical plug comprising the aerosol-forming substrate, is retained by contact with the cigarette paper. Shrinkage of the aerosol-forming substrate during heating may mean that the aerosol-forming substrate, or a portion thereof, is more likely to be removed from the rod of the smoking article when the smoking article is withdrawn from the heating element. This would result in the need to clean the aerosol-generating device comprising the heating element before the aerosol-generating device could be used to smoke another smoking article. An aerosol-forming substrate that is stuck to a heating element will provide a physical barrier to the re-use of the heating element as it may prevent the heating element being inserted into a new smoking article. 
     It is also undesirable for small portions of aerosol-forming substrate and residues of aerosol-forming substrate to remain in contact with the heating element as these may decompose over prolonged heating and produce unpleasant flavours that are detectable by a user. 
     As used herein, the terms ‘aerosol-generating article’ and ‘smoking article’ refer to an article comprising an aerosol-forming substrate that is capable of releasing volatile compounds that can form an aerosol. For example, an aerosol-generating article may be a smoking article that generates an aerosol that is directly inhalable into a user&#39;s lungs through the user&#39;s mouth. An aerosol-generating article may be disposable. 
     As used herein, an aerosol-generating article is a heated aerosol-generating article, which is an aerosol-generating article comprising an aerosol-forming substrate that is intended to be heated rather than combusted in order to release volatile compounds that can form an aerosol. The aerosol formed by heating the aerosol-forming substrate may contain fewer known harmful constituents than would be produced by combustion or pyrolytic degradation of the aerosol-forming substrate. An aerosol-generating article may comprise, a tobacco stick. 
     As used herein, an ‘aerosol-generating device’ relates to a device that interacts with an aerosol-forming substrate to generate an aerosol. The aerosol-forming substrate forms part of an aerosol-generating article, for example part of a smoking article. An aerosol-generating device may comprise one or more components used to supply energy from a power supply to an aerosol-forming substrate to generate an aerosol. 
     An aerosol-generating device may be described as a heated aerosol-generating device, which is an aerosol-generating device comprising a heater. The heater is preferably used to heat an aerosol-forming substrate of an aerosol-generating article to generate an aerosol. 
     An aerosol-generating device may be an electrically heated aerosol-generating device, which is an aerosol-generating device comprising a heater that is operated by electrical power to heat an aerosol-forming substrate of an aerosol-generating article to generate an aerosol. An aerosol-generating device may be a gas-heated aerosol-generating device. An aerosol-generating device may be a smoking device that interacts with an aerosol-forming substrate of an aerosol-generating article to generate an aerosol that is directly inhalable into a user&#39;s lungs thorough the user&#39;s mouth. 
     As used herein, the term ‘aerosol-forming substrate’ relates to a substrate capable of releasing volatile compounds that can form an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate. An aerosol-forming substrate may be adsorbed, coated, impregnated or otherwise loaded onto a carrier or support. An aerosol-forming substrate may conveniently be part of an aerosol-generating article or smoking article. 
     An aerosol-forming substrate may comprise nicotine. An aerosol-forming substrate may comprise tobacco, for example may comprise a tobacco-containing material containing volatile tobacco flavour compounds, which are released from the aerosol-forming substrate upon heating. In preferred embodiments an aerosol-forming substrate may comprise homogenised tobacco material, for example cast leaf tobacco. 
     The specification relates to a smoking article and a method of using a smoking article. In one embodiment, a smoking article comprising a plurality of elements, including a front-plug and an aerosol-forming substrate, is provided. The front-plug defines a hole or slit through which a heating element may be inserted. 
     The smoking article may comprise a rod. In one embodiment, the plurality of elements, including the front-plug and the aerosol-forming substrate are assembled in contact with a cigarette paper to form the rod. The rod can be defined as having a mouth end and a distal end located upstream from the mouth end. The front-plug is located upstream of the aerosol-forming substrate within the rod. 
     In use, a user applies his or her lips to the mouth end of the rod and inhales. Air and any aerosol generated within the rod are drawn through the mouth end of the rod to be inhaled by the user. When the user inhales, air and aerosol move through the rod in a direction generally from the distal end to the mouth end of the rod. In some embodiments, air may be drawn into the rod through the distal end of the rod. In some embodiments, air may be drawn into the rod through a sidewall of the rod. In other embodiments, air may be drawn into the rod through a combination of the distal end of the rod and a sidewall of the rod. 
     For simplicity, the terms “upstream” and “downstream” as used herein refer to a relative position along the rod of the smoking article with reference to the direction in which the aerosol is drawn through the rod. Any element or component that is closer to the distal end from a particular reference point can be defined as upstream from that point. Likewise, any element or component that is closer to the mouth end from a reference point can be defined as downstream from that point. In this embodiment, the front-plug is located closer to the distal end of the rod than the aerosol-forming substrate. Thus, the front-plug can be defined as being upstream of the aerosol-forming substrate. 
     In some embodiments, the smoking article may comprise further elements. For example, the article may further comprise a filter, such as a mouthpiece filter, located downstream of the aerosol-forming substrate. Preferably, such a filter is located at the mouth end of the rod. If present, a filter is preferably assembled along with the front-plug and the aerosol-forming substrate in the rod. Suitable filters may be made from any suitable filter material. Many such filter materials are known in the art, for example a suitable filter may be made from a length of cellulose acetate tow. Other elements such as free-flow filters and spacers may also be assembled with the front-plug and the aerosol-forming substrate as part of the smoking article. 
     Preferably, the elements forming the smoking article are assembled within a cigarette wrapper to form a rod. A suitable cigarette wrapper may be a cigarette paper or may comprise tobacco. Suitable cigarette wrappers are known in the art. 
     One advantage of the front-plug is that it may prevent egress of the aerosol-forming substrate from the distal end of the rod during handling and shipping. Another advantage of the front-plug is that it may assist location of the aerosol-forming substrate at a predetermined distance from the distal end of the rod for optimum engagement with a heat source such as a heating element. 
     Preferred embodiments are smoking articles for use with an aerosol-generating device comprising one or more heating elements that are configured to contact the aerosol-forming substrate. For the avoidance of doubt, in the following description the term heating element is used to mean one or more heating elements. 
     It may be preferable for the heating element to contact or penetrate the aerosol-forming substrate. In such embodiments, the aerosol-forming substrate may shrink into contact with a heating element during an aerosol-generating phase. The aerosol-forming substrate may also shrink such that its contact with the cigarette paper is reduced. Without a front-plug, the withdrawal of the heating element from the rod may also result in the withdrawal of the aerosol-forming substrate due to increased adhesion of the aerosol-forming substrate with the heating element coupled with decreased adhesion of the aerosol-forming substrate with the cigarette paper. However, the front-plug may facilitate removal or extraction of the heating element from the rod by restricting the movement of the aerosol-forming substrate towards the distal end of the rod. The front-plug blocks the passage of the aerosol-forming substrate and therefore prevents the aerosol-forming substrate from being withdrawn from the rod. 
     The front-plug may be made from a filter material that allows air to be drawn through the front-plug. The front-plug may conveniently be formed from the same material as a conventional mouthpiece filter. For example, the front-plug may be formed from a length of cellulose acetate tow. Permeability of the front-plug may be varied to help control resistance to draw through the smoking article. Alternatively, the front-plug may be formed from a material that is not permeable to air, although some air may be drawn through the hole or slit defined in the front-plug, depending on tolerances between the hole or slit and a heating element inserted therethrough. 
     The front-plug may comprise one or more materials selected from the group comprising ceramic, polymer, biopolymer, metal, zeolite, paper, cardboard, inert material, and inorganic material. The front-plug has a diameter that is approximately equal to the diameter of the smoking article. Preferably, the front-plug has a diameter between about 5 millimetres and about 10 millimetres. The front-plug has a length that may be defined as the dimension along the longitudinal axis of the smoking article. The length of the front-plug may be between about 1 millimetre and about 10 millimetres, for example between about 4 millimetres and about 8 millimetres. It is preferred that the front-plug is substantially cylindrical has a length of at least 2 millimetres in order to facilitate assembly of a smoking article, preferably at least 3 mm or at least 4 mm. A longer plug may also provide an improved cleaning effect as there is a greater amount of the front plug material available for wiping the heating element as the heating element is withdrawn from the plug. It is preferable that the diameter of the plug is greater than 5 mm, for example between 6 mm and 8 mm. 
     In some embodiments, the front-plug may be partially or entirely formed from an aerosol-forming substrate. For example, the aerosol-forming substrate may be a material comprising tobacco or processed tobacco and the front-plug may comprise this material. If an aerosol-forming substrate is incorporated in the front-plug, the density of the aerosol-forming substrate may be increased at the distal end of the rod to allow the aerosol-forming substrate to function as a front-plug. 
     Some embodiments of the smoking article are designed to be used in conjunction with an aerosol-generating device having a heating element for heating the aerosol-forming substrate. Such heating elements are typically in the form of pins or blades that can be inserted into the smoking article through the front-plug. To facilitate this, the hole or slit defined through the front-plug may be dimensioned to facilitate the insertion of a heating element. A heating element is then able to contact or penetrate the aerosol-forming substrate with a low insertion force required to penetrate the front-plug. For example, the size and shape of the hole defined through the front-plug may almost exactly match the size and shape of a cross-section of the heating element. 
     The hole may have smaller dimensions than the heating element, or may be a slit. In such embodiments, the heating element may need to deform the material of the front-plug in order to penetrate the front-plug. Any hole defined through the front-plug may be cylindrical or prismatic in shape. For example, the hole defined through the front-plug may be shaped like a circular cylinder or a hexagonal cylinder. Any slit defined through the front-plug may be a single slit or multiple slits. 
     The material forming the front-plug may be a resilient material or a partially resilient material that may be deformed by insertion of a heating element and regain its shape when the heating element is removed. Thus, where a heating element is of similar dimensions, or slightly greater dimensions, to the hole or slit defined through the front-plug, the material of the front-plug may deform to allow access to the heating element. When the heating element is removed, the hole or slit through the front-plug may regain its previous dimensions. An advantage of such embodiments may be that the material forming the front-plug may wipe the heating element as the element is withdrawn from the smoking article. This may help remove any fragments of the aerosol-forming substrate that have adhered to the heating element, and may help clean any volatile compounds that have been deposited on the heating element. The heating element may, therefore, be cleaned every time the heating element is removed from a smoking article. 
     The front-plug does not need to be formed from a resilient material in order to provide cleaning functionality. For example, if a hole through a front-plug is dimensioned to almost exactly match a cross-section of a heating element, then some cleaning functionality may be provided on withdrawal of the heating element. Likewise, if the front-plug defines a slit through which the heating element may pass the front-plug material surrounding the slit is deflected when a heating element is inserted. Subsequent withdrawal of the heating element may also result in interference between the heating element and the material surrounding the slit, which may provide cleaning or wiping of the heating element. 
     The front-plug may have more than one hole or slit defined through it. For example, if the smoking article is intended to be used with an aerosol-generating device having three heating pins, the front-plug of a compatible smoking article may comprise three holes arranged to accept the passage of the heating pins. 
     The aerosol-forming substrate may be a solid aerosol-forming substrate. Alternatively, the aerosol-forming substrate may comprise both solid and liquid components. The aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavour compounds, which are released from the substrate upon heating. Alternatively, the aerosol-forming substrate may comprise a non-tobacco material. The aerosol-forming substrate may further comprise an aerosol former. Examples of suitable aerosol formers are glycerine and propylene glycol. 
     If the aerosol-forming substrate is a solid aerosol-forming substrate, the solid aerosol-forming substrate may comprise, for example, one or more of: powder, granules, pellets, shreds, spaghetti strands, strips or sheets containing one or more of: herb leaf, tobacco leaf, fragments of tobacco ribs, reconstituted tobacco, homogenised tobacco, extruded tobacco and expanded tobacco. The solid aerosol-forming substrate may be in loose form, or may be provided in a suitable container or cartridge. Optionally, the solid aerosol-forming substrate may contain additional tobacco or non-tobacco volatile flavour compounds, to be released upon heating of the solid aerosol-forming substrate. The solid aerosol-forming substrate may also contain capsules that, for example, include the additional tobacco or non-tobacco volatile flavour compounds and such capsules may melt during heating of the solid aerosol-forming substrate. 
     Optionally, the solid aerosol-forming substrate may be provided on or embedded in a thermally stable carrier. The carrier may take the form of powder, granules, pellets, shreds, spaghetti strands, strips or sheets. Alternatively, the carrier may be a tubular carrier having a thin layer of the solid substrate deposited on its inner surface, or on its outer surface, or on both its inner and outer surfaces. Such a tubular carrier may be formed of, for example, a paper, or paper like material, a non-woven carbon fibre mat, a low mass open mesh metallic screen, or a perforated metallic foil or any other thermally stable polymer matrix. 
     The solid aerosol-forming substrate may be deposited on the surface of the carrier in the form of, for example, a sheet, foam, gel or slurry. The solid aerosol-forming substrate may be deposited on the entire surface of the carrier, or alternatively, may be deposited in a pattern in order to provide a non-uniform flavour delivery during use. 
     In preferred embodiments the aerosol-forming substrate comprises one or more sheets of homogenised tobacco material that has been gathered into a rod, circumscribed by a wrapper, and section to provide individual plugs of aerosol-forming substrate. 
     Although reference is made to solid aerosol-forming substrates above, it will be clear to one of ordinary skill in the art that other forms of aerosol-forming substrate may be included in other embodiments. For example, the aerosol-forming substrate may be a liquid aerosol-forming substrate. If a liquid aerosol-forming substrate is provided, the aerosol-generating device preferably comprises means for retaining the liquid. For example, the liquid aerosol-forming substrate may be retained in a container. Alternatively or in addition, the liquid aerosol-forming substrate may be absorbed into a porous carrier material. The porous carrier material may be made from any suitable absorbent plug or body, for example, a foamed metal or plastics material, polypropylene, Terylene (polyethylene terephthalate), nylon fibres or ceramic. The liquid aerosol-forming substrate may be retained in the porous carrier material prior to use of the aerosol-generating device or alternatively, the liquid aerosol-forming substrate material may be released into the porous carrier material during, or immediately prior to use. For example, the liquid aerosol-forming substrate may be provided in a capsule. The shell of the capsule preferably melts upon heating and releases the liquid aerosol-forming substrate into the porous carrier material. The capsule may optionally contain a solid in combination with the liquid. 
     Alternatively, the carrier may be a non-woven fabric or fibre bundle into which tobacco components have been incorporated. The non-woven fabric or fibre bundle may comprise, for example, carbon fibres, natural cellulose fibres, or cellulose derivative fibres. 
     The smoking article may be substantially cylindrical in shape. The smoking article may be substantially elongate. The smoking article may have a length and a circumference substantially perpendicular to the length. The aerosol-forming substrate may be substantially cylindrical in shape. The aerosol-forming substrate may be substantially elongate. The aerosol-forming substrate may also have a length and a circumference substantially perpendicular to the length. The aerosol-forming substrate may be received in the aerosol-generating device such that the length of the aerosol-forming substrate is substantially parallel to the airflow direction in the aerosol-generating device. 
     The smoking article may have a total length between approximately 30 millimetres and approximately 100 millimetres. The smoking article may have an external diameter between approximately 5 millimetres and approximately 12 millimetres. The smoking article may comprise a filter or a mouthpiece. The filter may be located at the downstream end of the smoking article. The filter may be a cellulose acetate filter plug. The filter is approximately 7 millimetres in length in one embodiment, but may have a length of between approximately 5 millimetres to approximately 14 millimetres. 
     In one embodiment, the smoking article has a total length of approximately 45 millimetres. The smoking article may have an external diameter of approximately 7.2 millimetres. Further, the aerosol-forming substrate may have a length of approximately 10 millimetres. Alternatively, the aerosol-forming substrate may have a length of approximately 12 millimetres. Further, the diameter of the aerosol-forming substrate may be between approximately 5 millimetres and approximately 12 millimetres. The smoking article may comprise an outer paper wrapper. Further, the smoking article may comprise a separation between the aerosol-forming substrate and the filter plug. The separation may be approximately 18 millimetres, but may be in the range of approximately 5 millimetres to approximately 25 millimetres. 
     In another embodiment, a method of using, consuming or smoking a smoking article comprising a plurality of elements is provided. The elements include a front-plug and an aerosol-forming substrate. The method involves the steps of inserting a heating element into the smoking article through a hole or slit defined through the front-plug, raising the temperature of the heating element to heat the aerosol-forming substrate sufficiently to form an aerosol, and withdrawing the heating element from the smoking article. 
     The aerosol generated by heating the aerosol-forming substrate may be inhaled by the user. The rod can be defined as having a mouth end and a distal end located upstream from the mouth end. Typically, a user applies his or her lips to the mouth end of the rod and inhales at the same time as the aerosol-forming substrate is heated by the heating element. Air and any aerosol generated within the rod are drawn through the mouth end of the rod to be inhaled by the user. 
     In some embodiments, the heating element is brought into direct contact with the aerosol-forming substrate, and in some embodiments, the heating element is inserted into the aerosol generating substrate. As described above, the aerosol-forming substrate may adhere to the heating element. The aerosol-forming substrate may also contract after heating and become loose within the rod. In such circumstances, the aerosol-forming substrate is susceptible to being withdrawn from the rod when the heating element is withdrawn. Thus, the method may provide a step in which the front-plug prevents egress of the aerosol-forming substrate as the heating element is withdrawn from the smoking article. The aerosol-forming substrate may move within the rod towards the front-plug and impinge the front-plug. This impingement may allow the adherence between the heating element and the aerosol-forming substrate to be overcome, thereby allowing the heating element to be withdrawn from the smoking article. 
     As described above, fragments of aerosol-forming substrate may adhere to the heating element. Furthermore, residues of the aerosol-forming substrate or residues derived from the aerosol-forming substrate may be deposited or formed on the heating element. The method may involve a step in which a surface of the heating element is wiped as the heating element is withdrawn from the smoking article. The ability to wipe a surface of the heating element on the front-plug may be a particular advantage where the front-plug defines a slit. Such wiping is effected by interference between a surface of the heating element and the material forming the front-plug. 
     The heating element will typically be a heating element of an aerosol-generating device compatible with the smoking article. Features described in relation to one embodiment may also be applicable to other embodiments. For example, the method of using a smoking article may be used in conjunction with any smoking article described above. 
    
    
     
       Specific embodiments will now be described with reference to the figures, in which; 
         FIG. 1  is a schematic cross-sectional diagram of a smoking article according to a first embodiment engaged with an aerosol-generating device; 
         FIG. 2  is a schematic diagram illustrating a front-end projection of the smoking article according to the first embodiment, showing penetration of the smoking article, through a slit defined in a front-plug, by a heating element; 
         FIG. 3A  is a schematic diagram illustrating a front-end projection of a smoking article according to a second embodiment, showing penetration of the front-plug of the smoking article by a heating element; and 
         FIG. 3B  is a schematic diagram illustrating a front-end projection of a smoking article according to a third embodiment, showing penetration of the front-plug of the smoking article by a heating element. 
     
    
    
       FIG. 1  illustrates a smoking article  1  according to a first embodiment. The smoking article  1  comprises five elements, a front-plug  2 , an aerosol-forming substrate  7 , a hollow cellulose acetate tube  6 , a transfer section  4 , and a mouthpiece filter  3 . These five elements are arranged sequentially and in coaxial alignment and are assembled by a cigarette paper  5  to form a rod  15 . The rod has a mouth-end  20 , which a user inserts into his or her mouth during use, and a distal end  30  located at the opposite end of the rod  15  to the mouth end  20 . Elements located between the mouth-end  20  and the distal end  30  can be described as being upstream of the mouth-end  20  or, alternatively, downstream of the distal end  30 . 
     When assembled, the rod  15  is 52 millimetres long and has a diameter of 7.2 millimetres. 
     The front-plug  2  is a cylindrical portion of cellulose acetate tow having a length of 7 millimetres. The fibres of the cellulose acetate tow are aligned with the longitudinal direction of the rod  15 . The front-plug  2  defines eight slits  23  that extend radially from a common point located centrally on an end face of the front-plug  2 . The eight slits  23  are angularly separated from each other by 45 degrees and extend through the front-plug  2 . As opposing slits are angularly separated by 180 degrees and effectively form a single slit, an alternative way to describe the same arrangement of slits would be four slits that are angularly spaced that intersect at a common point centrally on an end face of the front-plug  2 . 
     The aerosol-forming substrate  7  is located downstream of the front-plug  2  and comprises a bundle of crimped cast-leaf tobacco wrapped in a filter paper. The cast-leaf tobacco includes additives, including glycerine as an aerosol-forming additive. 
     The tube  6  is located immediately downstream of the aerosol-forming substrate  7  and is formed from cellulose acetate. The tube  6  defines an aperture having a diameter of 3.3 millimetres. One function of the tube  6  is to locate the aerosol-forming substrate  7  towards the distal end  30  of the rod  15  so that it can be contacted with a heating element. The tube  6  acts to prevent the aerosol-forming substrate  7  from being forced along the rod  15  towards the mouth-end  20  when a heating element is inserted. 
     The transfer section  4  comprises a thin-walled tube of 18 millimetres in length. The transfer section  4  allows volatile substances released from the aerosol-forming substrate  7  to pass along the rod  15  towards the mouth end  20 . The volatile substances may cool within the transfer section  4  to form an aerosol. 
     The mouthpiece filter  3  is a conventional mouthpiece filter formed from cellulose acetate tow, and having a length of 7 millimetres. 
     The five elements identified above are assembled by being tightly wrapped within a cigarette paper  5 . The cigarette paper  5  in this specific embodiment is a conventional cigarette paper. For example, the cigarette paper may be a porous material with a non-isotropic structure comprising cellulose fibres (crisscross of fibres interlinked by hydrogen bonds), one or more fillers and one or more combustion agents. The one or more fillers may be, for example, calcium carbonate (CaCO 3 ) and the one or more combustion agents may be, for example, one or more of the following: potassium/sodium citrate; sodium acetate; mono-ammonium phosphate (MAP); and di-sodium phosphate (DSP). The final composition of the cigarette paper per square metre may be approximately 25 g cellulose fibres, 10 g calcium carbonate, and 0.2 g combustion agent. The porosity of the cigarette paper may be between approximately 0 Coresta and approximately 120 Coresta. The interface between the cigarette paper  5  and each of the elements locates the elements and defines the rod  15  of the smoking article  1 . 
     Although the specific embodiment described above and illustrated in  FIG. 1  has five elements assembled in a cigarette paper, it will now be clear to one of ordinary skill in the art that a smoking article according to the embodiments discussed here may have additional elements and these elements may be assembled in an alternative cigarette wrapper or equivalent. Likewise, a smoking article according to the embodiments discussed here may have fewer elements. Moreover, it will now be apparent to one of ordinary skill in the art that various dimensions for the elements discussed in relation to the various embodiments discussed here are merely exemplary, and that suitable alternative dimensions for the various elements may be chosen without deviating from the spirit of the embodiments discussed herein. 
     The smoking article of the first embodiment is consumed or smoked in conjunction with a suitable aerosol-generating device.  FIG. 1  illustrates the smoking article when engaged with such a device  11  for consumption. 
     The aerosol-generating device  11  comprises a sheath  12  for receiving the smoking article  1  for consumption. A heating element  8  is located within the sheath  12  and positioned to engage with the distal end  30  of the smoking article  1 . The heating element  8  is shaped in the form of a blade terminating in a point  40 . 
     As the smoking article  1  is pushed into the sheath  12  the point  40  of the heating element  8  engages with one or more of the slits  23  defined through the front-plug  2 . The heating element  8  is blade-shaped, its width being greater than its thickness. The smoking article  1  may need to be rotated by an angle of up to 22.5 degrees to correctly align with a slit or pair of slits  23 , as these are angularly separated by 45 degrees. By applying a force to the smoking article  1  once the blade is engaged with a slit  23 , the heating element  8  is inserted through the slit  23  and penetrates the front-plug  2 . Material forming the front-plug  2  deforms to allow the heating element  8  to be inserted, and contact is maintained between the front-plug  2  and a surface of the heating element  8 . 
     As the heating element  8  is inserted further into the smoking article  1 , the point  40  of the heating element  8  contacts the plug of aerosol-forming substrate  7 . The application of further pressure causes the heating element  8  to penetrate into the aerosol-forming substrate  7 . Once the optimum engagement position has been reached, further penetration is prevented as the distal end  30  of the smoking article  1  abuts an end wall of the sheath  12 , which acts as a stop. 
     When the smoking article  1  is properly engaged with the aerosol-generating device  11 , the heating element  8  has been inserted through the front-plug  2  and is located within the aerosol-forming substrate  7  in contact with aerosol-forming material. An insulating collar  9  may surround a portion of the heating element  8  that is in contact with the front-plug  2 . The collar  9  may alternatively be a cool zone provided on the length of the heating element  8 . Such a collar may prevent the heating element  8  from burning or melting the front-plug  2 . 
       FIG. 2  is a front-end view of the smoking article  1  when engaged with the heating element  8 . This view shows the cigarette paper  5  in contact with the front-plug  2 . The heating element  8 , which can be seen to have a blade shaped cross-section, has been inserted through slits  23  extending through the front-plug  2 . The heating element  8  has deformed the cellulose acetate material forming the front-plug  2  slightly on passing through the slits  23 , and the resilience of this cellulose acetate material results in contact between the front-plug  2  and outer surfaces of the heating element  8 . 
     The aerosol-generating device  11  comprises a power supply and electronics (not shown) that allow the heating element  8  to be actuated. Such actuation may be manually operated or may occur automatically in response to a user drawing on the smoking article  1 . When the heating element  8  is actuated, the aerosol-forming substrate  7  is heated and volatile substances are generated or evolved. As a user draws on the mouth end  20  of the smoking article  1 , air is drawn into the smoking article  1  and the volatile substances condense to form an inhalable aerosol. This aerosol passes through the mouth-end  20  of the smoking article  1  and into the user&#39;s mouth. 
     The heating element  8  is heated to a temperature of about 375 degrees Celsius in order to generate an aerosol from the aerosol-forming substrate  7 . As volatile substances are driven off the aerosol-forming substrate  7  by heat, the aerosol-forming substrate  7  dries out and shrinks. This can result in the aerosol-forming substrate  7  gripping the heating element  8 . Simultaneously, the shrinkage of the aerosol-forming substrate  7  may cause a loss in contact with the cigarette paper  5 . In the first embodiment the aerosol-forming substrate  7  is in the form of a plug, and the shrinkage causes this plug to become loose within the rod  15  of the smoking article  1 . 
     After use, the user withdraws the smoking article  1  from the aerosol-generating device  11 . The smoking article  1  is withdrawn from the sheath  12  and the heating element  8  slides out of the front-plug  2 . Because the adherence between the heating element  8  and the aerosol-forming substrate  7  is greater than the adherence between the aerosol-forming substrate  7  and the cigarette paper  5 , the aerosol-forming substrate  7  moves towards the distal end  30  with the heating element  8 . However, the front-plug  2  blocks the path of the aerosol-forming substrate  7 . This allows the heating element  8  to be withdrawn from the aerosol-forming substrate  7  without removing the aerosol-forming substrate  7  from the smoking article  1 . 
     Particles of the aerosol-forming substrate  7  or residues derived from the aerosol-forming substrate  7  may become stuck to the heating element  8  during operation. As the heating element  8  is withdrawn from the smoking article  1 , the outer surface of the heating element  8  is wiped by the front-plug  2 . Thus, the heating element  8  is automatically cleaned by wiping every time a smoking article  1  is removed from the aerosol-generating device  11 . 
     The first embodiment described above with reference to  FIGS. 1 and 2  describes a smoking article  1  having its distal end closed by a front-plug  2  that has a plurality of through slits  23 . Such a front-plug  2  requires a heating element  8  to be forced through the slits  23  defined through the front-plug  2  to contact the aerosol-forming substrate  7 . 
     A second embodiment of a smoking article  100  is illustrated in  FIG. 3A  (end view only). The smoking article  100  of  FIG. 3A  is identical to the smoking article  1  of the first embodiment described above apart from the configuration of the front-plug  102 . The front-plug  102  is formed from cellulose acetate and is assembled in contact with a cigarette paper  5 , but the front-plug  102  defines a substantially circular through-hole  103  allowing through-access to a heating element of an aerosol-generating device. The heating element can pass through the front-plug  102  with minimal insertion force required. The circular shape of the hole  103  means that there is no special orientation relationship required between the smoking article  100  and the heating element in order to engage the smoking article  100  with the aerosol-generating device. 
     In use, the front-plug  102  of the smoking article  100  acts in the same way as described above to prevent egress of an aerosol-forming substrate from the smoking article  100 . 
     A third embodiment of a smoking article  300  is illustrated in  FIG. 3B  (end view only). The smoking article  300  of  FIG. 3B  is identical to the smoking article  1  of the first embodiment described above apart from the configuration of the front-plug  302 . The front-plug  302  is formed from cellulose acetate and is assembled in contact with a cigarette paper  5 , but the front-plug defines a star-shaped hole  303  allowing through-access to a heating element of an aerosol-generating device. The hole  303  lowers the insertion force required to insert a heating element into the smoking article  300 . The star-shape of the hole  303  allows the heating element to engage with the front-plug  302  of the smoking article  300  and prevent rotation of the smoking article  300  while it is being consumed. 
     In use, the front-plug  302  of the smoking article  300  acts in the same way as described above to prevent egress of an aerosol-forming substrate from the article. 
     The exemplary embodiments described above are not limiting. In view of the above discussed exemplary embodiments, other embodiments consistent with the above exemplary embodiments will now be apparent to one of ordinary skill in the art.