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A bed sheet is a rectangular cloth used to cover a mattress and those sleeping upon it. They are the sheets which one typically lies 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.
The term bed sheet was first used in the 15th century. Bed sheets were traditionally white but now various colours and patterns are used.
Bed sheets come in two main varieties: flat or 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.
Usually a flat bed sheet is overlocked around the edges to form four seams. One of the seams is wider than the other three and helps with orienting the sheet correctly on the mattress. The wider seam goes at the head end of the mattress. Sometimes the sides do not have seams, but are finished with the selvedge only. When placing a flat sheet on a bed, the manufacturer has designed the printed side to be softer, and thus it should be placed on the bed printed side "down". When folding back the covers, this also allows the printed side to show, for aesthetic purposes. When one makes a bed, the patterned or monogrammed side of the top sheet is placed facing down and then the top edge is folded towards the foot of the bed, exposing the design.
Common materials used to create bed sheets include cotton, linen, satin, silk, rayon, bamboo fibre, Polyproplyne spunbond, and blends of cotton with polyester. 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.
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