A Bed Sheet is a rectangular cloth used to cover a mattress and those sleeping upon it. They are the sheets which one typically lays between. In many places a second flat bed sheet is laid on top of the sheet covering the mattress. When a second sheet is used, the top one is known as the top sheet and the sheet covering the mattress is known as the bottom sheet or "coupie sheet" in some European countries. If the bottom sheet is presewn to fit snugly over the mattress, it is known as a fitted sheet. Blankets, quilts, duvets, comforters and other bed covers are placed on top of the top sheet.
Common materials used to create bed sheets include cotton, linen, satin, silk, rayon, bamboo fibre, polypropylene spunbond, and blends of cotton with polyester. Some new materials, such as nonwoven polypropylene fabric, allow the sheet to be disposable due to their low price. Disposable sheets are typically used in emergency shelters or hospitals, and sometimes in hotels.
The quality of bed sheets is often conveyed by the thread count-the number of threads per square inch of material. In general, the higher the thread count, the softer the sheet, but the weave and type of thread may affect the "hand" of the material so that a sheet with a lower thread count may actually be softer than one with a higher count. Yarn quality also plays a part in the look and feel of sheets, as finer yarns tend to create a finer sheet fabric.