Lightweight and technical, the Sea to Summit Spark Ultralight 40F sleeping bag is designed to keep you as warm as possible while minimizing packed weight and size.
Fill
850+ UltraDry Down
Temperature Rating (F)
40 degrees (F)
- Superlight 7-denier and 10-denier fabrics offer minimal weight and packed size
- 850+ fill-power Premium Goose UltraDry Down™ certified to the Responsible Down Standard (RDS) and provides maximum insulation value
- Contoured mummy shape provides comfort and efficient insulation
- Vertical chest baffles prevent down migration
- Note: This bag is not designed to zip with another
Imported.
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.
View all Sea to Summit Backpacking Sleeping BagsEach 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.
| Best Use | Backpacking |
|---|---|
| Tested Lower Limit | 40 degrees (F) - EN |
| Tested Comfort | 48 degrees (F) - EN |
| Temperature Rating (F) | 40 degrees (F) |
| Temperature Rating (C) | 5 degrees (C) |
| Ultralight | Yes |
| Shell | 10-denier nylon |
| Zipper Location | Left |
| Insulation Type | Down |
| Water-Resistant Down | Yes |
| Fill | 850+ UltraDry Down |
| Lining | 7-denier nylon |
| Sleeping Bag Shape | Mummy |
| Stuff Sack Size | Unavailable |
| Stuff Sack Volume | Unavailable |
| Compressed Volume | Unavailable |
| Gender | Unisex |
| Sustainability | Down certified to the Responsible Down Standard (RDS) |