You've all had this happen. You tear a piece of sand paper in half and then fold it over on itself so you have a quarter sheet for sanding what ever. After a while the grit still has plenty of life left but the backing paper is falling apart so you toss it. The way I prevent this from happening is to use spray on contact cement. Fold the half sheet of sand paper so you have a nice crease. Then open it up and spray on the contact cement (on the paper side of course). Fold over again and there ya go. The paper holds up much better this way and cause the contact is very flexible the sand paper is still easily formed to molding or what have ya.