A duvet is a soft, flat bag filled with down, feathers, wool, cotton, silk, or synthetic alternatives, typically protected by a removable cover. Originating in rural Europe, duvets were traditionally filled with the down feathers of ducks or geese, with the eider duck's feathers being particularly valued for their thermal insulation properties. The term "duvet" is of French origin, meaning "down feather," and was first mentioned in English in 1759. In the UK, prior to the 1970s, a similar form of bedding was called an eiderdown. In Australia, the term "doona" is commonly used, derived from the Danish word "dyne," meaning eiderdown. Duvets are popular in Europe and Australia, while in the United States, they are often referred to as comforters or quilts.