What is a Duvet? A duvet is a soft, flat bag filled with down or synthetic fibers. The name refers to this insert and is sold separately from duvet covers or other coordinating bed linens. If you hate making the bed, a duvet with a cover can be used instead of a top sheet and blanket, which can save time and stress. While a duvet cover should be machine washable, duvets themselves are usually dry-cleaned.