the duvet is the actual comforter itself (like goose down or sythetic or whatever) and they are usually just plain white, not decorative. then the duvet cover is the decorative thing that you put over it. i like having this setup instead of a regular comforter because it's so much easier to just remove and clean a duvet cover than a whole bulky comforter.
I agree that it's easier to clean, but it's just such a pain to keep the comforter straight in the cover. Unless, of course, you decide to safety pin the corners, etc.
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