Manufactured cigarettes in Australia consist of a rod of cut tobacco and a crimped cellulose acetate filter wrapped in porous paper. At the mouth end of the cigarette there is another layer of non-porous paper, called tipping paper, which is typically around 30mm in length. There may also be various additives used to facilitate manufacture, increase shelf life, improve flavour and aroma and control burn mechanics, nicotine delivery and harshness/ irritation.
In about 90% of Australian brands, the tipping paper contains perforations– known as filter ventilation–to dilute the smoke with fresh air when the smoker takes a puff (see Figure 12.4.1).1 This inconspicuous feature turns out to be highly important for the purpose of creating variety in taste strength and harshness/ irritation, and it was also a crucial feature for creating variation in tar, nicotine and carbon monoxide yields during the period when Australian brands carried this information on the packs or it was publicised in 'tar tables'.1
Photograph of filter tipping paper showing filter vents
Filter ventilation is the primary means by which the taste strength and harshness of Australian manufactured cigarettes is varied, followed by the use of filters of differing densities and lengths.1 When filter ventilation level is increased, the density or length of the filter is usually also increased so as to keep the overall draw resistance of the cigarette within the range that smokers prefer. Longer and/ or denser filters generally have higher filtration efficiency and the combined effects of increased filtration and increased ventilation are to make the smoke more dilute so it tastes weaker or 'milder' and produces less harshness (the immediate burning/ scratching sensations in the mouth and throat) and irritation (the lingering tingling sensations in the throat and chest).
Varying filter ventilation levels and filtration efficiencies was also the principal means of varying the standard ISO tar, nicotine and carbon monoxide yield figures of Australian brand varieties prior to the end of yield labelling in March 2006.1 Where a particular brand 'family' had multiple varieties with differing tar, nicotine and carbon monoxide yields, variations in filter ventilation levels and filtration efficiency were the main engineering features used to produce the yield variations.1
Filter ventilation and filtration efficiency respectively determine the amount of smoke generated per puff at the burning tip and the proportion of smoke generated which passes through the cigarette filter to be inhaled by a smoker or collected by a smoking machine filter in yield testing 2 . Other means of varying standard ISO tar and nicotine yields include varying tobacco rod length, tobacco rod density, paper porosity and paper additive levels 2. These latter means are used more to reduce the number of puffs taken by the smoking machine than to reduce the amount of tar and nicotine generated per puff.2 Varying nicotine levels in tobacco is a potential means of varying nicotine yields and of varying nicotine yields relative to tar yields, although as will be shown below, the available evidence is that low nicotine yield cigarettes do not have low nicotine levels in the unburned tobacco rod.1,3
Prior to the introduction of filter ventilation in Australia some time around 1973, the lowest standard ISO tar yield that was possible for a cigarette that would gain any level of consumer acceptance was around 7mg.1 The lowest tar yield possible for a cigarette with mass consumer acceptance was approximately 10–12mg. After filter ventilation became a standard feature of Australian cigarettes, it became possible to produce cigarettes with standard ISO tar yields of 1mg, which would be consumed by commercially viable numbers of smokers.1 By the mid 1990s, '8mg or less' had become the most popular tar yield category in the Australian market and the sales-weighted average tar yield was 6mg.1
Filter ventilation is a crucial design feature of 'low tar' cigarette brands that facilitate compensatory smoking (which are referred to within the tobacco industry as brands with high 'delivery elasticity' or 'consumer demand responsiveness'). Filter ventilation rewards smokers' efforts to either gain larger amounts of dilute smoke or to gain more concentrated smoke than is gained when those cigarettes are machine tested using the standard ISO yield test.2,4
If per-puff machine-tested tar and nicotine yields are reduced by increasing filtration efficiency, the cigarettes will have increased draw resistance. This provides a barrier to smokers' attempts to get more tar and nicotine per puff by taking bigger puffs. Eventually the effort of drawing large puffs from high draw resistance cigarettes becomes aversive.1,4 However, if per-puff machine tested tar and nicotine yields are reduced by increasing filter ventilation, the cigarettes will have reduced draw resistance. That means it will be easier to take either larger puffs or more rapidly drawn ones (which has the effect of reducing both filtration efficiency and filter ventilation level). However, it is not necessary to take very large puffs to get substantially more smoke from filter ventilated cigarettes. Another common means of compensatory smoking is for smokers to unconsciously block the filter vents with their fingers or lips, thus reducing the amount of fresh air being taken with each puff. Because vent blocking increases smoke concentration, it makes the smoke taste stronger. This suits many smokers who want stronger tasting cigarettes but also prefer to smoke cigarettes that labelled 'smooth or 'fine' (or previously were labelled 'light' or 'mild').
In summary: filter ventilation creates multiple opportunities for compensatory smoking so smokers can learn the compensatory smoking behaviours that best suit them.4 However, this generally does not occur deliberately. It should be noted that most smokers take large puffs and/ or block vents without any awareness that they are doing so. They are usually well aware of the smoke being less irritating and weaker-tasting but unaware of the mechanisms through which those sensations of 'mildness' arise.4 Consequently, many smokers continue to believe the tobacco in 'smooth' and 'fine' brands is different to that in 'original' brands (ie: the strongest tasting brands).
1. King B and Borland R. The 'low tar' strategy and the changing construction of Australian cigarettes. Nicotine & Tobacco Research 2004;6(1):85–94. Available from: http://www.informaworld.com/smpp/content~db=all?content=10.1080/14622200310001656907
2. Kozlowski L, O'Connor R and Sweeney C. Cigarette design. In: Risks associated smoking cigarettes with low machine-measured yields of tar and nicotine Smoking and Tobacco Control Monograph. Bethesda, Maryland: US Department of Health and Human Services, Public Health Service, National Institutes of Health 2001. Available from: http://cancercontrol.cancer.gov/tcrb/monographs/13/
3. Kozlowski LT, Mehta NY, Sweeney CT, Schwartz SS, Vogler GP, Jarvis MJ, et al. Filter ventilation and nicotine content of tobacco in cigarettes from Canada, the United Kingdom and the United States. Tobacco Control 1998;7(4):369–75. Available from: http://tobaccocontrol.bmj.com/cgi/content/full/7/4/369
4. Kozlowski L and O'Connor R. Cigarette filter ventilation is a defective design because of misleading taste, bigger puffs, and blocked vents. Tobacco Control 2002;11(suppl.1):i40-i50. Available from: http://tc.bmjjournals.com/cgi/content/abstract/11/suppl_1/i40