Sea to Summit  Trek TkII 18 Sleeping Bag

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With a tapered rectangular shape that offers more room than a mummy bag, the Sea to Summit Trek TkII sleeping bag keeps you warm via water-resistant, RDS-certified 650-fill-power down.


  • Water-repellent, 650-fill-power Ultra-Dry Down™ retains 60% more loft and absorbs 30% less moisture than untreated down; down is also PFC-free and RDS-certified
  • Responsible Down Standard (RDS) ensures the down does not come from animals that have been subject to any unnecessary harm, such as force-feeding or live-plucking
  • Tapered rectangular shape offers more space than a traditional mummy bag while maintaining thermal efficiency
  • Nylon shell fabric is treated with a durable water repellent (DWR) finish that sheds moisture and helps block wind
  • Vertical chest baffles prevent down migration and 3D sidewall baffle maximizes loft right to the edge of the bag to prevent cold spots
  • 2-way #5 YKK® side and foot zippers let you ventilate as needed; oversized zip draft tube keeps out the drafts, while antisnag materials make for smooth zipping
  • 3D hood draws in tight to keep you cozy; neck collar draft tube seals in warmth
  • 20-denier lining fabric is lightweight and soft on your skin
  • Internal security pocket keeps nighttime essentials close at hand
  • Comes with an Ultra-Sil™ compression sack and a nylon storage sack
  • This bag is designed to zip together with another to create a double bag


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 #152789
Best Use


Tested Lower Limit

18 degrees (F) - EN

Tested Comfort

30 degrees (F) - EN

Temperature Rating (F)

18 degrees (F)

Temperature Rating (C)

-7.8 degrees (C)


30-denier nylon

Zipper Location


Insulation Type


Water-Resistant Down



650-fill-power Ultra-Dry down


20-denier nylon

Sleeping Bag Shape


Stuff Sack Size





Down certified to the Responsible Down Standard (RDS)

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