Duvet covers often have buttons, ties, an envelope flap, or zipper as a closure to keep the insert enclosed. It should be noted that a Duvet is the insert that goes inside the Duvet Cover; usually comprised of down or a down alternative. When the insert and duvet cover are together, sometimes it is referred to as a Comforter. It is common for Duvet Covers to have finishing details like flanges or embroidery along the side and bottom edges only.