Hi, Welcome to the board. I use muslin or any other good cotton fabric. When I startead quilting 40+ years ago I wasn't aware of fabric that came wider than 44 " wide. I learned the hard way not to use sheets if you are a hand qulter. Sheets especially ones that are not 100% cotton are too tightly woven. I like to use cotton flannel on the backs of children's quilts or lap robes for those who are chair or bed bound. The flannel helps to keep the quilts from sliding off of a person's lap and they make them very cuddly for small children. The flannel can take the place of having batting if you just want something to cover a lap without being real heavy. I make lap robes for amputee soldiers with just a flannel back and no batting. They mostly want to hid their injuries from visitors. It makes both they and their guests more comfortable.