A Duvet is just like a pillowcase, except larger. Many cultures, especially the Europeans commonly use them. They buy a single comforter- often with the best down filling- that they then cover with a duvet as simply as they use a pillowcase. Sometimes a lot of money is invested in the quality of these comforters which can be reused for many years or even generations by simply changing the duvet which is washed regularly with the pillowcases and the bottom sheet. Obviously, the decor can also be changed easily without sacrificing the money on ALL new bedding. It makes a lot of economical and “green” or conservation sense. Plus, it is just about the most comfortable way to sleep.