A bed sheet is a rectangular piece of cloth used either singly or in a pair as bedding, being placed immediately below or above bed occupants. A top sheet, in the many countries where they are used, is a flat sheet, immediately under which bed occupants lie. A bottom sheet is laid above the mattress and bed occupants lie on it. A bottom sheet may be either a flat sheet, or a fitted sheet, which has been sewn to form a large pocket around the top, sides and bottom edge of a mattress, with elastic or a drawstring in the hem to stop it slipping off the bottom of the mattress. Blankets, quilts, duvets, comforters and other bed covers are laid over the top sheet.
Cotton and cotton blends dominate the market. The most common blend being cotton and polyester. Cotton provides absorbency and a soft hand, while polyester adds durability and wrinkle resistance. Other common fibers used in the manufacturing of bed sheets include linen, silk, Modal and bamboo rayon, lyocell, and polypropylene. Polypropylene (olefin) is a hypoallergenic spun-bound material produced at a low cost and typically used in emergency shelters or hospitals as disposable sheeting.
Bed sheets come in two main varieties: flat and fitted. A flat sheet is simply a rectangular sheet of cloth, while a fitted sheet has its four corners, and sometimes two or four sides, fitted with elastic, to be used only as a bottom sheet. The fitted sheet may also be secured using a drawstring instead of elastic. The purpose of a fitted bottom sheet is to keep it from slipping off the mattress while the bed is in use. A particular way of folding and tucking while making the bed, known as “hospital corners,” is sometimes used when the bottom sheet is flat rather than fitted.