Reactor Fleece Liner

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The THERMOLITE® Reactor™ Fleece liner is Sea to Summit’s warmest sleeping bag liner. Add one to your sleeping bag before heading into really cold environments  or, use as a 'stand alone' sleeping bag when the weather is warmer. The hollow core THERMOLITE® fibers have the same hollow structure as polar bear – when made into a fleece, this traps a lot of insulating air. Luxuriously soft, the Reactor Fleece is perfect as part of a cold weather sleep system – plus it will help keep your sleeping bag clean.

Learn more about which liner is right for you HERE.


  • Work for backpacking? It may. The 14.2oz weight is a very reasonable trade-off for its thermal performance, and the packed volume of 2.5 Liters is impressively small. Weight-conscious performance users may opt for a Spark Liner or Flame Liner.
  • Add 32°F / 18°C to any sleeping bag? Not necessarily. There are a lot of factors involved in the thermal performance of a sleep system, starting with the insulation value of your sleeping pad. Read more HERE.
  • Need special care when being washed? No! The Reactor Fleece Liner can be washed in a washing machine with normal supermarket laundry ‘soap’ and dried in a dryer, using cool or low heat. Fabric softeners will reduce wicking performance of the fabric.