For my own curiousity, I went to the Kasho site Mooman suggested above.

I translated (through babelfish) a bit of the Kasho site's explanation:


Genuine zelluloid has to be replaced evenly by nothing. Most Plektren is nowadays from plastics. But some few manufacturers still hold to zelluloid. It sounds simply better. It lends the completely special crack to the notice. And it looks animal good. This material was invented 1864 by the brothers Hyatt and has not much with plastics to do, rather with wood. Wood is to forty per cent from cellulose, and this cellulose affects the sound more than other components of the wood. From the cellulose of the wood in one to complicate procedure the zelluloid is won. Kampfer, alcohol and cotton are further components. Thinly finished it is relatively problem-free. Still today of it motion picture films are manufactured. That is very difficult thicker things to process and needs alone for drying a half year! Kasho from Okinawa in Japan is one of the few still thereby delivers itself. Richly thereby in Japan their remaining will do nobody and the incomprehensible environmental regulations. But by a license agreement we can get Kasho Plecs, and at a very good price. Hopefully remains still for a long time in such a way...

Translation software has a long way to go...