Sea to Summit Spark Ultralight Sleeping Bag Liner

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Built for fast-and-light adventures, this Sea to Summit Spark Ultralight sleeping bag liner is a great pick for summer overnights or boosting your sleeping bag's warmth on chillier trips.


  • 7-denier shell and 7-denier liner materials help to achieve an impressively light weight and compact packed size
  • 850-fill-power down provides cozy warmth
  • Sewn-through quilted construction makes this an incredibly light and compact bag
  • 1/3-length zipper
  • Includes lightweight Ultra-Sil™ compression bag and storage cell


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 Bags

Technical Specs

Best Use


Tested Comfort

50 degrees (F) - ISO

Temperature Rating (F)

50 degrees (F)

Temperature Rating (C)

10 degrees (C)




7-denier nylon

Zipper Location


Insulation Type


Water-Resistant Down



Ultra-dry down


7-denier nylon

Sleeping Bag Shape




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