I often get the question, 'is duvet cover a comforter?’ Or, 'what's the difference between a duvet cover and a comforter?'
Short answer is, 'no, a duvet cover is not a comforter'. 
duvet cover is an envelope that is used for covering a comforter for whole bunch of reason. Including the fact that, it keeps the comforter clean. Also because duvet covers are relatively inexpensive and come in variety of colors, designs and patterns. Therefore, it’s very easy to change them, wash them and match them according to your mood, walls, drapes, or even the carpet. 
That said, what’s the difference between the two? 
It’s very easy to remember, one is filled with soft down and offers warmth and comfort - thus the word comforter. The other one covers the comforter and therefore, called duvet cover.