Duvet cover set includes 1 duvet cover +2 pillow sham A duvet cover encases and protects a duvet. Like an envelope, it has an opening where the comforter or duvet is inserted. Once placed inside, the opening is closed with a zipper. Duvet covers are generally very decorative and are available in a wide selection of colors and styles. The duvet cover takes the place of a top sheet in the U.S.