The flat sheet, also called the highest sheet, was originally placed between the sleeping person and their blanket. Now that a lot of folks use duvet covers, flat sheets are usually wont to make your bedding feel more welcoming. consider it as an additional layer of heat and softness as you slumber. It also protects the blanket or the comforter from getting dirty. On warmer nights the flat sheet is often employed by itself rather than a blanket.