Flat sheets are large pieces of fabric, typically made from cotton, polyester, or a blend, used in bedding. They serve as a top layer on a mattress, providing comfort and protection. Flat sheets come in various sizes, including twin, full, queen, and king, to fit different bed dimensions. Unlike fitted sheets, which have elastic corners to hug the mattress, flat sheets are simply laid on top. They can also be used for other purposes, such as picnic blankets or table covers. Flat sheets are often part of a complete bedding set, which may include pillowcases and a duvet cover.