Sea to Summit Spark Ultralight Sleeping Bag 5

The Sea to Summit Spark Ultralight Sleeping Bag 5 is the winter-rated member of the Spark line, built for fast-and-light trips into sub-zero temperatures. An EN/ISO 23537-tested comfort rating of -8°C and limit of -15°C put it firmly in cold-weather territory, yet it weighs only 880 g — a weight-to-limit figure of 58.7 g/°C that is competitive for this temperature range. The low weight comes from 620 g of 850 fill power goose down at a 90/10 ratio, treated to stay hydrophobic so loft holds up in damp conditions. Box-baffle construction keeps fill evenly distributed and limits cold spots, while a 10D shell and 7D liner shave further grams. A full-length zipper with draft collar and draft tube, plus a fitted, contoured hood, cuts down on heat loss during the coldest hours. Sized for users up to 183 cm, the bag can zip to a second one for double-bag use. The down is RDS-certified and the treatment is PFC-free. It suits winter treks and alpine trips where every gram counts, though the ultralight fabrics demand careful handling.