Absence of Combustion in the IQOS Tobacco Heating System

Heat-not-Burn concept

Research has demonstrated that the majority of the harmful and potentially harmful constituents (HPHCs) detected in cigarette smoke are largely formed by the thermal breakdown of tobacco when it is burned. Philip Morris International’s (PMI) heated tobacco products are designed to generate a nicotine-containing aerosol by heating tobacco to temperatures sufficient to release nicotine and flavors from the tobacco but low enough to prevent the tobacco from burning. The concept behind ‘Heat-not-Burn’ is that heating tobacco, rather than burning it, can significantly reduce the levels of HPHCs generated, whilst retaining a satisfactory sensory experience for adult smokers.

Fig. 1. Thermochemical processes as function of temperature.

When heated to temperatures below the onset of combustion, the tobacco undergoes a number of thermochemical processes, such as drying, evaporation, torrefaction, and low temperature pyrolysis, as shown in Fig. 1 . For combustion of the tobacco to occur, the temperature needs to exceed around 400 °C/752 °F 1 , and three elements must be present: a fuel to be burned, an oxidant (usually the oxygen in air) to oxidize the fuel, and an ignition source (a flame or spark) to initiate the reaction. Combustion (burning) is an exothermic chemical process of oxidation that occurs at a rate fast enough to produce heat and usually light. 2


In a cigarette, combustion occurs when the tobacco is ignited by a heat source, such as the flame from a match or a lighter. Once lit, a self-sustaining exothermic oxidation reaction is established at the tip of the burning cigarette with the tobacco reaching temperatures above 850 °C/1562 °F) 3. The heat released by the combustion process breaks down tobacco leaf components generating smoke and leaves an ash residue. The cigarette smoke formed contains more than 6,000 chemicals,4 some of which have been classified by public health authorities as likely causes of smoking-related diseases, such as lung cancer, heart disease and emphysema.


The IQOS tobacco heating system is based on the heat-not-burn concept: heating tobacco without combustion. As depicted in Fig. 2 , IQOS consists of three distinct components that perform different functions: (i) a novel patented tobacco stick containing a specially processed tobacco material made from tobacco powder, water, glycerol, guar gum, and cellulose fibers (ii) a holder into which the tobacco stick is inserted and which heats the tobacco material by means of an electrically controlled heater, and (iii) a charger that is used to recharge the Holder after each use.

Fig. 2. Components of the IQOS

Tobacco temperature in the Tobacco Stick

The electrically controlled heater in the holder is programmed to reach temperatures between 320 °C/608 °F and 350 °C/662 °F (Fig. 3), and if its operating temperature exceeds 350 °C/662 °F, the energy supply to the heater is cut off. Temperature measurements, using thermocouples inserted in the tobacco stick at different radial distances from the heater during product use, show that the tobacco touching the heater surface reaches a maximum temperature of 320 °C/608 °F (Fig. 3). This is well below the temperatures required for combustion of the tobacco to occur (known to exceed 400 °C/752 °F). Already at 0.2 mm from the heater, the temperature is reduced to below 250 °C/482 °F.

Fig. 3. Temperatures measured in the Tobacco Stick during use at different radial distances (R) from the heater surface together with the programmed heater profile. Solid black lines show the average temperatures, while the colored regions show the ranges between the minimum and maximum temperatures of 5 replicates for each position.

Contrary to the increase in the temperature that occurs when air is drawn through a lit cigarette (rising from around 600 °C/1112 °F to above 850 °C/1562 °F)3, there is a significant drop in the temperature of the tobacco in the tobacco stick when a puff is taken as the air cools the tobacco. In contrast to the exothermic self-sustaining combustion process in a cigarette, the heating of tobacco in the IQOS demonstrates a net endothermic behavior, i.e. thermal energy generated by the heater is required to heat up the tobacco and to maintain its temperature. When the heater is switched off, the temperature of the tobacco immediately drops.

Experiments in absence of air

The IQOS tobacco heating system was also tested in a chamber filled with air and in a chamber filled only with nitrogen, where one of the essential elements needed for combustion (oxygen) was absent. The levels of aerosol collected revealed that the chemical markers of tobacco combustion were statistically equivalent under both atmospheres, providing additional data supporting the absence of combustion of the tobacco in the tobacco stick during use.a

Absence of ash

When tobacco sticks are heated in the IQOS holder, they are not consumed by combustion processes, no ash residue is visible, and they retain their structural integrity.


Several robust scientific experiments have confirmed the absence of combustion of the tobacco in tobacco sticks when heated in the IQOS holder. Due to the controlled operating temperature of the heater, the aerosol generated is formed principally by the water, nicotine and glycerol evaporated from the tobacco substrate. As the tobacco is heated and not burned, the aerosol has on average 90 to 95% lower levels of HPHCs compared to the smoke from a standard reference cigarette (3R4F).b The absence of combustion in tobacco sticks, when used as intended in IQOS holder, has been verified by scientific experts in numerous countries, including Italy, the United Kingdom, Japan, Poland, the United States, Australia, and Germany, as well as by an independent research organization in New Zealand.5


1. Barontini, et al., (2013) Volatile Products Formed in the Thermal Decomposition of a Tobacco Substrate. Industrial & Engineering Chemistry Research 2013 52 (42), 14984-14997

2. National Fire Protection Association (NFPA). (2018). NFPA Glossary of Terms 2018 Edition. NFPA.

3. Baker, R.R., (1975) Temperature variation within a cigarette combustion coal during the smoking cycle; High Temperature Science 7: 236–247.

4. Rodgman, A. and Perfetti, T.A., (2013) The Chemical Components of Tobacco and Tobacco Smoke. 2nd Edition. CRC Press, Boca Raton.

5. CRL Energy Ltd., Investigation into iQOS device, HEETS tobacco sticks and evidence of combustion. Report N° 17/11019. Issued on November 17, 2017. 2017.

a. Health Canada Intense (HCI) machine-puffing protocol (55 mL puff volume, 2 s puff duration, 30 s puff interval)

b. Average of the reductions in the concentrations (weight per stick) of individual HPHCs measured in the IQOS aerosol compared to the smoke from the standard 9.4 mg reference cigarette (3R4F). Aerosol and smoke collections performed under the HCI machine-puffing regime. Reduction calculations exclude nicotine.