Perhaps C.T. Rodgers or another coin storage supply dealer can explain it better than I, Mark, as I only go by looks, feel and odor. If you've ever cut a piece of PVC pipe with a saw, you will detect the same odor of PVC flips and stock books. I also detect the slightly blueish oily film on the flips when held up to a light which isn't always easy to see. Also, the "safe" flips are mostly labled as such and they are more brittle than the plyable PVC type and also break in two real easy. The older PVC types are in the marketplace, but I can't answer your question: "are there a lot being sold?" I don't know. I suggest visiting a coin shop that sells storage supplies to see and feel both types. You may also want to try doing a search on "coin storage supplies" to find additional information with e-mail addresses. This s the best I can do.

JB