I use stiff card stock that is acid free 12 X 12 folded in half, and they work for me and soo much cheaper, I probably have more that 300 of them, I also wrap the fat quarters, so all of my fabric fits and is displayed nicely. They provide enough stiffness to sit vertically on the shelf, better when shelf is full, but I don't find that as a problem. I wouldn't wrap my fabric on anything that isn't acid free.