A flat bed sheet is the rectangular top sheet that is placed over the sheet covering the mattress. It protects the comforter and blanket from dirt and grime and is used in place of a blanket on warmer nights.
A flat bed sheet, also called the top sheet, serves a decorative purpose apart from protecting the bed from dirt. Printed bed sheets that complement interior décor make a bed look more inviting. It is a good idea to place a designed flat bed sheet on the mattress with its printed side down and to fold back the top edge toward the foot to reveal the design.
Flat sheets are over-clocked around the edges to form seams on all four sides. Wider seams at one side of the bed sheets indicate the side that goes to the head end of the mattress. Loom-woven or flat-knitted bed sheets are finished with selvage instead of seams at the edges. Flat sheets are flat and fold easily. Size is not a crucial factor with these sheets, and a double bed sheet can be used on a queen-sized bed or vice versa. Larger sheets are tucked in on the sides and bottom of the bed, under the comforter.