Sea to Summit  Spark SpI Sleeping Bag

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Packing down to the size of a 1-liter water bottle, this ultralight bag balances size, weight and warmth to make it an excellent choice for summertime backpacking, cycle touring and mountaineering.


  • High-loft, premium 850-fill-power European goose down offers superb warmth with minimal weight; Ultra-Dry Down™ water-repellent treatment protects down from moisture
  • Ultra-Dry Down is a water-repellent polymer treatment applied to the down; Ultra-Dry Down retains 60% more loft and absorbs 30% less moisture than untreated down
  • With a European Norm (EN) lower-limit rating of 46°F, the Sea to Summit Spark SpI will help keep you warm on 3-season backpacking adventures in warm weather
  • You can also use the Spark Sp I as a booster bag by slipping it inside another sleeping bag to add warmth
  • Ultralight 10-denier Pertex® Quantum® fabric with a durable water repellent treatment sheds moisture
  • Soft 15-denier nylon fabric lines the sleeping bag for excellent comfort next to skin
  • Left-side 1/3-length zipper saves weight over a full-length zipper
  • Compresses to the size of a grapefruit
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

Item #866773
Best Use



Tested Lower Limit

46 degrees (F) - EN

Tested Comfort

54 degrees (F) - EN

Temperature Rating (F)

46 degrees (F)

Temperature Rating (C)

8 degrees (C)




Ripstop nylon

Zipper Location


Insulation Type


Water-Resistant Down



850-fill goose down



Sleeping Bag Shape


Stuff Sack Size

4 x 9 inches

Stuff Sack Volume

2.5 liters

Compressed Volume

1.55 liters



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