What's Duvet Cover? A duvet cover is essentially a fabric bag for a comforter. It works almost the way a pillowcase covers a pillow. The only difference: A duvet cover is typically closed with buttons, zippers, or ties. Duvet covers do two jobs: First, they make it easier to keep your comforter clean. You won't need to wash your comforter very often, just wash the cover regularly. (this is important, because down comforters should only be washed every one to three years). And second, as one of the largest visual elements in the bedroom, they serve as a key anchor for the room's overall style, and happily one that's easy to change when you're ready for a new look.