Unless it is for a child, I use unbleached muslin. I like the look and feel of it. for the kids, I use something that coordinates with the front. I have also used sheets, but not a lot. I do use the bleached muslin when I am lucky enough to find it at a yard sale or am gifted it, but there is just a special feel to the unbleached that I really like. In the end, it is just whatever you are happy with.