A comforter is a cover for a bed that's made up of stuffing placed between two layers of fabric, whereas a duvet is a thick comforter specifically stuffed with natural or synthetic feathers or down. A duvet is often placed inside a cover and is designed to be used on the bed without sheets. The cover not only adds extra warmth but can be taken off and washed separately.
Comforters that are not duvets can be stuffed with polyester batting, cotton, silk or wool. The thickness of the filling is known as the loft, and it determines whether the comforter is lightweight, medium weight or extra warm. Some manufacturers also make comforters that are light as regular blankets for use in the summer. Generally, regular comforters are laid over the top of the other bedclothes.
Comforters are also stitched in different ways. These stitches make the comforter both more aesthetically pleasing and keep the filling from bunching up in one area of the comforter. The stitches include the ring stitch, the channel and box stitch and the karo stitch. The karo stitch is not as formal as the other stitches and allows the stuffing to shift around a bit to conform to the sleeper's body.