Spark 45F Down Sleeping Bag

Count on a great night’s sleep while counting grams with the Sea to Summit Spark 45F sleeping bag. It’s warmed with 850+ fill-power down, and the 10-denier shell sheds wind and condensation.

Temperature ratings are intended as a guideline to help you compare products, rather than a guarantee of warmth, since many different factors contribute to your comfort while you sleep. Backpacking bags are typically rated for temperature according to an independent testing protocol—currently International Organization for Standardization (ISO) 23537, though some older items followed European Norm (EN) 13537. Testing is based on a person wearing one base layer and a pair of socks, sleeping on an insulated surface with a minimum R-value of 5.38.

Each bag then gets 2 ratings: the Comfort rating is the lowest temperature at which the bag will keep the average “cold sleeper” comfortable, and the Lower Limit rating is the lowest temperature at which the bag will keep the average “warm sleeper” comfortable. Some brands determine their own temperature rating by aligning to the Comfort rating for women’s bags, to the Lower Limit rating for men’s bags, or somewhere in the middle for nongendered bags.