We used to pay extra for the cotton filter tubes, but I have no clue what they actually were made of, I think I noted this somewhere when someone was all a dither about the purity of their wick because all you need to know about cigarette filters and their goodness for you would be to peer down at any busy intersection and check out the cigarette butts discarded there.
I would imagine animals get at them and whatnot and somehow. Etc.
I also am not a believer in the "tar bar" extra filtration systems, and they remind me of many "as seen on TV" products that remain in use due to the simple fact of "curiosity." They don't work.
Anna