The same,when the covers are made,allowances are made for the insertion of a duvet.....
In europe, the duvet is the down comforter itself. Usually the duvet doesn't have quilting -- the lines of stitching that make separate compartments for the down. It's more like a bed-sized cotton bag filled with down.
I bought a down comforter years ago and have just bought "duvet" covers when I changed my color scheme and I bleach it once a week to make sure that it has no mites, or anything growing in there. It is white and bleachable and i would recommend you d...