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 sheets 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.