avoid sheets with a high thread count (over 200) as most quilting cottons are thread counts in the 40-70 range. A high thread count sheet will shrink very differently and is hard to needle through, causing thread shredding and skips on the long arm. If a client brings me one, I ask for low thread count, wash and pressed, and if they have taken out the hems and expect that fabric to be part of the backing, they need to prep them carefully.