I use sheets all the time for backings, Ross is my go-to for them! I've done flannel, 100% cotton and the cotton/poly blend. What's frustrating is that now more and more sheets are the microfiber 100% poly and I'm not a fan of them for backs, I'm sure they would work fine but I just don't like the feel. I do always pre-wash the sheet in hot to make sure it's shrunk.