Belledorm Premium Blend 500 Thread Count Flat Sheet. This flat sheet is made from a premium blend of 67% Cotton and 33% Polyester, offering the natural benefits of cotton with the easy-care properties of polyester. It features a silky sateen weave with highly packed fabric for a soft feel. The high thread count ensures a luxurious and durable fabric that is easy to wash and maintain, remaining wrinkle-free wash after wash. This King size flat sheet is the best of both worlds, combining luxury with practicality. Brand: Belledorm. Washable. 67% Cotton 33% Polyester.