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Sea to Summit Thermolite Reactor Extreme Liner


Availability: Out of Stock

Item # STSKA203
Increasing the warmth of your sleeping bag (sold separately) by as much as 25 degrees Fahrenheit (14 Degrees Celsius), the Sea to Summit Thermolite Reactor Extreme Liner is perfect for the backpacker looking for versatility to venture out into the coldest of temperatures.
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Increasing the warmth of your sleeping bag (sold separately) by as much as 25 degrees Fahrenheit (14 Degrees Celsius), the Sea to Summit Thermolite Reactor Extreme Liner is perfect for the backpacker looking for versatility to venture out into the coldest of temperatures.

The liner utilizes 110 gram Hollow core fiber Thermolite fabric and a mummy-cut to provide next to skin comfort and maximize thermal efficiency. An integrated footbox further ensures comfort.

The full dimensions of the Sea to Summit Thermolite Reactor Extreme Liner are 84” x 36” and it weighs 14 ounces. It packs down to 4” x 6” in the included sil-nylon stuff sack.

  • 110g/m2 Thermolite construction throughout
  • Adds up 25°F (14°C) to warmth to a sleeping bag
  • Mummy shape with a box foot
  • Draw cord hood with mini cord lock
  • Packs into its own Ultra-Sil stuff sack
  • Dimensions: 84 in / 210cm x 36 in / 90cm



Best Use Backpacking, Camping, Travel
Item Weight 14.0 oz
Other Stuff Sack Included
Warranty Limited Lifetime
Packed Size 4" x 6"
Shell Material 110 gram Hollow core fiber Thermolite


Real Customer Reviews

Average Rating:
(based on 10 real customer reviews)

10 Items

Great quality, not sure it keeps you any warmer though.
Reviewed by Billy P - January 16, 2019

Likes: It protects your sleeping bag from trail dirt, sweat, and grime. It is very well made and material is very comfortable/stretchy.

Dislikes: I'm not sure it actually keeps you noticeably warmer. After using it on two backpacking trips (both in the 40's°F) I was still a little chilly at night. I would rather have just brought a warmer sleeping bag. It's also a little pricey, in my opinion.

Surprisingly warm
Reviewed by Amanda C. - November 14, 2018

Likes: Feels like slinky pajama material, and just as warm and cozy.

Dislikes: Wish it were a few less ounces but I'd rather carry a few extra ounces than be cold!

Well Made
Reviewed by Andrew K. - August 31, 2018

Likes: This liner has good stitching. It is roomy. It will not restrict like the smaller compact model. This is more compact than the fleece.

Dislikes: The fleece model is about 10 degrees warmer, and has a zipper.

Warm when you need it to be.
Reviewed by Gabriel H. - July 14, 2018

Likes: Lightweight
Can be it’s own sleeping bag on warmer nights

Dislikes: Drawstring is awkward

It's just what I've been missing!
Reviewed by Anthony D. - May 11, 2018

Likes: Had a chance to try this out recently as the Michigan winter that just hasn't wanted to leave gave me a chance. Temps a little below freezing with ice pellets, snow and freezing rain made for miserable conditions. I used this inside of my Marmot Phase 20 Degree bag, and I was totally comfortable all night. I can see where this will be perfect for a stand alone bag in warmer temps too, and it'll keep the inside of my bag from getting trashed with trail grunge. Happy with the packed down size, and the extra couple of ounces in weight are well worth the comfort of a good night's sleep.

Dislikes: None.

A new necessity
Reviewed by Jeff K. - April 23, 2018

Likes: Purchased to use with my Lamina Z Spark sleeping bag. I had an instance last October where the lows hit the upper 30/low 40's and my feet were very cold so I needed something to help keep warm.

I was finally able to test the liner out this weekend. It's lightweight and has a very soft feel. Recently took this liner camping with overnight lows floating around 32. Worked as advertised to keep my body (and more importantly feet) warm. I can't vouch that it was a 25 degree difference, but it definitely helped me to stay warm and comfortable throughout the night.

Dislikes: N/A

Gets the Job Done
Reviewed by Scott T. - April 10, 2018

Likes: Great alternative to a sleeping bag in warmer weather. Has insulating properties that stand alone or adds to an existing bag. Fits nicely in the Kelty Cosmic Tall.

Dislikes: None

lightweight piece of gear used to extend the backpacking season, or as a stand alone cover for warm summer trips
Reviewed by Chris K. - December 1, 2017

Likes: soft/durable

Dislikes: wish it packed down a little smaller

Backcountry Edge's service was great
Reviewed by Juan Q. - August 25, 2017

Likes: comfortable, lightweight

Dislikes: nothing

Good liner to protect your bag
Reviewed by David - April 25, 2017

Likes: super soft liner, adds warmth, protects your sleeping bag from dirt, oils, etc

Dislikes: wish it was slightly longer, heavier than most other liners

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