In the world of bedding, the duvet cover is one of the most important pieces of furniture. This unique combination may not seem like a big problem, but it can really cause irritation when it doesn't fit properly. To clear any misunderstandings, let's look at the differences between duvets, comforters, and duvet covers. Duvets are soft and fluffy versions of a comforter in which, once filled, is ready to use as a complete cover for the bed. Comforters are full-sized sheets that have been sewn together into a blanket.