Here is a moderate winter bag that can be used comfortably in the Spring and Fall, yet it has been known to keep climbers warm on Denali. Most people can afford only one good sleeping bag, and usually you can only take one bag per trip. Unfortunately, most winter bags seem to be made to exclude other uses, forcing you to go too cold or too warm depending on where your bag lies on the temperature curve. We designed the Widgeon for the successful American 1990 K2 Expedition to be used alone at base camp and in conjunction with down clothing at their high camp. With a liner bag or down clothing, you could use the Widgeon on any summit attempt in the world. The removable collar and the ability to adjust the down gives a much wider temperature range than you would expect. Even by itself the Widgeon can cover a much broader range than any other single bag on the market. It also features continuous baffles, single draft tubes, a breathing tunnel, 3D contoured hood, and a removable collar.
(From the manufacturer)