I agree with Torrey regarding the 2×2 cardboard flips that you can write on with the mylar window. Mylar is an inert material and has no chemical reaction as does pvc. Gaming tokens too are affected by pvc. A greenish color sticky slime forms on the tokens after a long period of time which is all bUT imissile to, remove.. Collectors should examine their chips and tokens that have been stored in the soft pliable 2×2's for long durations.

Along with the cardboard 2×2 holders, the stiffer non pvc flips work fine too, but many chippers do not like them because they tend to be brittle and sometimes crack apart into two halves if handled frequently.