Sea to Summit Spark Ultralight 18F Sleeping Bag

Color: Gray
Size: Long
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Designed for late spring to early fall use, the Sea to Summit Spark Ultralight 18F sleeping bag is a lightweight pick for ounce-counting backpackers. It serves up easy ventilation and cozy comfort.


  • 850-fill-power down provides cozy warmth
  • Baffles in the torso area keep insulation in place; sewn-through construction in the leg area helps keep this bag lightweight
  • 10-denier shell and 7-denier liner materials deliver an impressively light weight and compact packed size
  • Full-length side zipper with 2 sliders offers easy ventilation options
  • Includes lightweight Ultra-Sil™ compression bag and storage cell


Many sleeping bags are rated for temperature by an independent testing protocol. REI and the broader industry now use the International Organization for Standardization (ISO) 23537 protocol, which improves on the older European Norm (EN) 13537 standard; you may still see older items in our assortment that were only EN tested. With either protocol, each bag gets a Comfort (or T-Comfort) rating and Lower Limit (or T-Limit) rating. 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. Ratings are based on a person wearing one long underwear layer and a pair of socks, sleeping on an insulated surface with a minimum R-value of 5.38. Many brands use the Comfort rating for women's bags and the Lower Limit rating for men's and unisex bags. Everyone's body and sleep comfort differ, and conditions of use (posture, clothing, sleeping pad R-value, wind, humidity, etc.) affect total insulation, so EN and ISO ratings are intended as a guideline to help you compare products, rather than a guarantee of warmth.
View all Sea to Summit Backpacking Sleeping Bags

Technical Specs

Best Use


Tested Lower Limit

18 degrees (F) - EN

Tested Comfort

29 degrees (F) - EN

Temperature Rating (F)

18 degrees (F)

Temperature Rating (C)

-8 degrees (C)


Long: 1 lb. 10 oz.




10-denier nylon

Zipper Location


Insulation Type


Water-Resistant Down



Ultra-dry down

Fill Weight

Long: 1 lb. 1.6 oz.


7-denier nylon

Sleeping Bag Shape


Fits Up To (in.)

Long: 78 inches

Shoulder Girth (in.)

Long: 64 inches

Hip Girth (in.)

Long: 56 inches

Stuff Sack Size

6 x 14 inches

Stuff Sack Volume

6 liters

Compressed Volume

Long: 5.4 liters



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