Many people like to use vintage sheets for quilting. On Etsy, there are several sites selling them cut into fat quarters. You can do a test on a scrap of the fabric using a match. Put a piece in an ashtray or something similar. Touch the lit match to the fabric. If it turns to ash, it should be all cotton. If it turns into a hard lump, there is some synthetic fiber in there, most likely polyester. Sheets from the 60s, 70s, and 80s are usually made with some polyester. We loved the no ironing aspect of it.