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THERMOLITE Reactor Extreme Liner (Adds up to 25°F)

The best way to make your sleeping bag warmer


Size Guide

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The THERMOLITE® Reactor™ Extreme is the warmest backpacking knit sleeping bag liner we offer. The hollow fiber threads work just like the hollow fur of a polar bear in that they trap heat effectively. When the mercury drops you'll appreciate the mummy shape and drawcord hood with mini cord lock attached. Depending on your environment and sleep conditions, this liner can increase your sleeping bag warmth by up to 25F. 

Learn more about which liner is right for you HERE


Packed Size Comparison

Similar to a red cup that is solo.


14 oz ≈ Lighter than a roll of paper towels


Adds up to 25°F to the temperature range of your sleeping bag.


Easy to wash and helps to keep your down bag cleaner for longer.


  • Adds up to 25°F / 14°C of warmth to a sleeping bag
  • Lighter weight, more packable than fleece
  • Mummy shape with a box foot
  • Drawcord hood with mini cord lock
  • Packs into its own Ultra-Sil™ stuff sack

Technical Features


The Reactor Series Sleeping bag liners, the Venture, Traverse and Basecamp synthetic Sleeping Bags and the foot boxes of the Women’s Altitude and Journey down Sleeping Bags use hollow core THERMOLITE® fiber to add warmth. These fibers trap extra air for insulation (just like the hollow-cores of polar bear or caribou fur).

In the liners, the knitted THERMOLITE® fabric is soft and stretchy and comes in three different weights: 80g/m² fabric used in the Reactor and the underside of the Compact Plus liners; a 110g/m² fabric which is used in the Extreme, and the core and foot box of the Compact Plus liner; and the Fleece, the warmest of all the fabrics.

THERMOLITE® is also used in the Air Sprung Cell sleeping mats.

Tech Specs

Product Details

Added Warmth
Up to 25°F / 14°C
Best Use
Backpacking, Camping & Winter Camping
Comes With
Ultra-Sil stuff sack
Thermolite polyester fabric
6 ft 10 in x 36 in / 210 x 92 cm
6.5 x 4.5 in / 17 x 11.5 cm
14 oz / 399 g

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