I use 2 layers of flannel--a design on one side and plain/coordinating on the other usually. I make mine as rectangles so they do lop over the top of the arm as spit-up usually ends up there! When I made bibs, I used the waterproof stuff--is it called pul?--on the back so moisture from food or drool doesn't leak through. It launders nicely and stays soft. I bought it at JoAnne's. I think it is commonly used for diaper covers by those who use cloth diapers.