Sea to Summit Alpine Down Winter Sleeping Bag -5

The Sea to Summit Alpine Down Winter Sleeping Bag -5 is a winter expedition mummy bag with EN ISO 23537 tested ratings — a comfort figure of -12°C and a limit of -20°C (extreme -42°C) place it in the 4-season winter category, meant for serious cold rather than mild shoulder-season nights. Insulation is 800 g of 850-fill-power goose down at a 90/10 down-to-feather ratio, hydrophobic-treated and RDS-certified. The NanoShell outer, a 20D recycled nylon with non-PFAS DWR, is also bluesign-certified. At a total weight of 1,340 g, the bag works out to roughly 67 g per degree of warmth — a solid figure for this temperature class. A contoured hood, draft collar and tube, and a two-way zipper are standard winter-bag features that limit heat loss while still allowing ventilation control. An internal pocket is a practical spot to keep a phone or power bank from freezing overnight. Suited to winter trekking and multi-day trips into genuinely cold conditions.