Sea to Summit Alpine Down Winter Sleeping Bag -40

The Sea to Summit Alpine Down Winter Sleeping Bag -40 sits at the top of the brand's warmth range, built for expeditions into high-altitude and arctic environments where a standard winter bag falls short. A manufacturer-rated comfort temperature of -30°C and limit of -40°C place it in the 5-season expedition category — a segment reserved for extreme conditions, not general winter backpacking. Insulation comes from 1,250 g of 850-fill-power goose down, among the highest fill power commonly available, which gives the bag a reasonable warmth-to-weight figure (roughly 46.8 g per degree) despite a total weight of 1,870 g. The down is hydrophobic-treated and RDS-certified, and the 20D recycled nylon shell carries a DWR finish. A 3D anatomical hood, two-way zipper, and draft collar and tube limit heat loss at the usual pressure points. This is a specialized tool for expedition and high-altitude winter use — for typical three-season trips it would be unnecessarily heavy and far warmer than needed.