Duvets reduce the complexity of making a bed, as it is a single covering instead of the combination of bed sheets, blankets, and quilts or other bed covers.
There is one thing very particular to them, that they do not cover themselves with bed-clothes.
The duvet itself fits into a specially made cover, usually of cotton or a cotton blend.
A modern duvet, like a sleeping bag, may be filled with down or feathers of various quality and cost, or silk, wool, cotton, or artificial fibers such as polyester batting.
Farethewell!