Duvets can reduce the complexity of making a bed, as they can be used without a top sheet, blankets or quilts or other bed covers. Duvets can be made warmer than blankets without becoming heavy. The duvet itself fits into a specially made cover, usually of cotton or a cotton-polyester blend. The duvet cover can be removed and laundered as often as the bottom sheet and pillow cases. The duvet itself may be cleaned much more rarely, and depending on its contents, may require specialist dry cleaning.