I saw leeching on some flips. While it did not appear to be enough to damage the chip, I took the hint.

I'm curious whether the flips supplied by the coin grading companies may be more stable - they seem less likely to have PVC in them, and they supply large flips for all coins (the customer sends them back in to protect the coin to be graded). Of course, I am not suggesting grading for chips - but rather whether it is a more stable material that we could look for. My preference, though, has been to use crown-size cardboard holders with mylar. I haven't had any trouble with those.