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Sea To Summit Thermolite Reactor Extreme


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. 


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

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