Hehe... Amazing that this comes up now, a week and a half after I start working for a company that MAKES DVD and game cases...
The card and comic holders that have PVC in them are made of Polyprolene and Polyurithane. Even the ones that say they are "PVC FREE" are not, they are sprayed with a coating that keeps the PVC from breaking down for a period of 6 to 18 months. The only way to get a true acid free protector for cards or comics is to get one made out of Mylar. The reason this proves a problem for comics and cards is because paper contians acid, and the ink used to print them also contains acid. Using a Mylar bag with a carbonite board helps to neutralize the acid from the paper and ink, preventing any yellowing.
That said, DVD and game cases are made out of Polyurithane and the clear covers that hold the paper inserts in place are usualy Polyprolene, though Polyurithane is also used. HOWEVER, the clear part of CD's and DVD's are also made of Polyurithane, so placing a Polyurithane part in a Polyurithane case doesn't really make any difference.
:banana