Flat sheets are large pieces of fabric, typically made from cotton, polyester, or a blend, used in bedding. They come in various sizes, such as twin, full, queen, and king, to fit different mattresses. Flat sheets serve as a top layer between the sleeper and blankets, providing comfort and warmth. Unlike fitted sheets, which have elastic corners to hug the mattress, flat sheets are simply rectangular and can be tucked in around the bed. They are often used in hotels and homes for easy washing and changing, contributing to a clean and fresh sleeping environment.