How to Spot a Psychopath

A reader writes:

Most cigarettes have a wrapping around the filter that looks like cork, because apparently the earliest filter cigs had a filter made of cork.

How the hell did that work, though?

Isn't cork used for, well, corks, because it's impermeable? How could you suck smoke through a cork? Perhaps smokers in 1940 were more health-conscious than we thought, and enjoyed these Unsmokable Health Cigarettes!

Luca

Today, most cigarette filters are made of cellulose acetate fibre, a substance of many uses (from cloth for garments to stuffing cushions) which is made by reacting plant cellulose with acetic acid.

But cigarette filters are, as you say, usually covered with a layer of paper printed with a cork pattern. And yes, that's because in the olden days the filters were made of cork. (This makes the printed-paper filter a "skeuomorph", an object with cosmetic design elements held over from an older version of the same thing.)

Cigarette filters were, however, never solid cork; as you say, that would be ridiculous. Instead, the filter was actually filled with loosely-packed cork granules, or a loosely-rolled piece of paper, which might itself have been made from cork.

There's nothing about cork that makes it a particularly excellent filter material. It was just a relatively cheap substance that wouldn't do anything very alarming if the smoker smoked all of the tobacco and sucked the flame back into the filter.

Cigarette filters have the peculiar task of blocking some bad stuff from getting into the smoker's lungs, without blocking the bad stuff that the smoker's paying to put into their lungs. (See also guns, which are generally designed to be simultaneously as safe, and as dangerous, as possible.)

So a really good filter material, like activated carbon, would be no use in a cigarette. Instead, filter materials with relatively low surface area are used. Activated carbon works so well as a purifying filter because it's immensely porous, giving it an enormous surface area per gram and allowing it to "adsorb" a surprising amount of stuff. Cellulose acetate fibres, of a similar consistency to cotton wool, adsorb rather more "tar" than the old cork filters, while letting various other compounds through.

Both cigarette filters and long cigarette holders do catch some particulate matter and "tar", but their actual effect on smokers' health is difficult to detect.

(See also "light" cigarettes that have air holes in the paper around the filter to dilute the smoke. In theory, they could actually be somewhat healthier than regular cigarettes, but in reality, there's no good evidence that "light" cigarettes are any better. Smokers cover the holes with their fingers, or just smoke more, or more deeply; however it happens, health outcomes are the same no matter what mainstream-Western-market cigarette you smoke.)

Psycho Science, as I have brilliantly decided to call it, is a new regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.