I've had many chips discolor some of my pvc flips such as the example Bob Orme had illustrated. I've never had this condition happen in the stiffer, non-pvc, 2x2" flips that break at the fold on occssion. The non-pvc flips are designed for use to be inserted in the 20 pocket three-ring pvc pages. I recall an article in Numismatic News some time ago by Susan Maltby that was published in which she described a simple test to determine which brands of 2x2's had pvc and which ones did not. It had to do with holding the flip over a flame and depending upon the color of the burning plastic would indicate a presence of pvc or not. Maybe one of our on-line chemists could tell us what color should a non pvc flip be when held over an exposed flame.