Duvets are usually filled with some type of feathering or synthetic alternative and it’s protected by a duvet cover. It’s easier to make your bed with a duvet because you usually don’t require additional layers to keep you warm.
Comforters are made to work with multiple bedding layers. They’re usually filled with synthetic fibres and stitched or quilted to evenly disperse its filling. You can also throw your comforter in the wash with the rest of your sheet set.