How Do Tar Filters Work? The Science of Cigarette Filtration
What is "tar" actually?
The word "tar" in the cigarette context is shorthand for the particulate residue of smoke once it condenses. It's not a single substance but a complex mixture — including polycyclic aromatic hydrocarbons (PAHs), phenols, tobacco-specific nitrosamines and other combustion products, many of them harmful.
Smoke also has a gas phase, with substances such as carbon monoxide. A purely mechanical filter catches particles but lets most gases through. That's why some filters combine two different stages.
Stage 1: Mechanical filtration
The first stage is usually a fibre material or a mesh. Particles larger than the gaps are physically blocked. Smaller particles can still be caught through three mechanisms known from aerosol physics:
- Interception — particles following an airstream brush against fibres and stick.
- Impaction — heavier particles can't follow the airstream around the fibres and hit them.
- Diffusion — very small particles move randomly (Brownian motion) and eventually hit a fibre.
This way a filter can catch particles across a range of sizes, not just those larger than the gaps. Design choices at this stage are always a trade-off: a denser filter catches more but makes the draw harder.
Stage 2: Activated carbon adsorption
Activated carbon is made from materials such as wood, coconut shell or coal that are heat-treated to create a very porous internal structure with a large inner surface. Gas-phase molecules that come into contact with these surfaces can stick to them — this is called adsorption.
Activated carbon can adsorb some of the gas-phase compounds that mechanical filters miss. It has essentially no effect on carbon monoxide. Not every two-stage filter uses activated carbon — check how the manufacturer describes the design.
Why two stages, not one bigger stage?
The temptation in filter design is to make one stage thicker or longer. Both have limits in practice: a thicker mechanical stage makes the draw much harder, and a longer stage adds length and resistance. Two shorter stages in series, each with its own job, are a common design approach.
A two-stage design is also used by Teerless: the first stage is designed to catch larger tar particles, the second is a finer filter stage. Together they are designed to trap tar residue that you can see in the used filter. We don't publish reduction percentages for it.
How efficient are filters really?
There's no single honest number. How much a filter catches depends on the filter, the cigarette and — above all — on how you smoke. Smoking machines use standardised puffs that don't match how people actually smoke, so machine-measured values say little about what a person inhales. These factors matter:
| Factor | Why it matters | What you can do | Limit |
|---|---|---|---|
| Fit | A loose filter lets smoke bypass it | Choose the right size | Only concerns the add-on filter |
| How you smoke | Deeper or more frequent puffs mean more smoke | Don't compensate by puffing harder | Hard to control consciously |
| Filter condition | A used filter collects residue | Replace it as recommended | Teerless: after up to 6 cigarettes |
| Gases | Gases such as carbon monoxide are not filtered mechanically | Smoke less or quit | No filter solves this |
That's why this site doesn't publish tar-reduction percentages for Teerless.
What filters can't do
Filters are an accessory, not a safety device. They don't address:
- Nicotine dependence — an add-on filter doesn't make smoke nicotine-free.
- Carbon monoxide — a gas that passes through mechanical filters and is not adsorbed by activated carbon.
- Compensatory smoking — smokers often inhale harder or more often when the draw changes, which works against any filter.
If you want to reduce harm, the most effective steps are smoking fewer cigarettes and quitting. Free help is available from quitlines, doctors and pharmacists.
Teerless two-stage filters
Regular (8 mm), Slim (6 mm, with adapters for 5 mm) and Slender+Slim (6.6–7.1 mm) — designed to trap tar residue you can see in the used filter.
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