I have used all types of sheets successfully, cotton, cotton/poly blends and flannel. They all machine quilt and wash and wear very well. Just make sure to press, starch if they tend to wrinkle and pin or baste well before quilting. Watch out for the really cheap sheets (we've had them here lately in Walmart) that have very low thread counts, wide weaves and feel a little rough as they won't stand up to frequent washings and probably wear out before your top.