Sheets are wonderful backs for quilts. I've used cotton, cotton/poly and flannel. All work well and there is no problem machine quilting them and they wear well. I stock up on patterned sheets when they are on sale and buy King sized ones so I will have extra fabric to make a matching pillow case. I usually can find them for $5-10 and the patterned ones hide less than perfect quilting. My son was with me the last time I bought 10 sheets and his comment was "Mom, how many mis-matched sheets does one family need?"