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Reactor Fleece Liner (adds up to 32°F)

Reactor Fleece Liner (adds up to 32°F)

Our warmest sleeping bag liner+ View tech specs
  • Shape
  • ColorGray

BEST USE: Backpacking & Camping

WEIGHT: 13.4 oz | 379 g

LENGTH: 6 ft 6 in | 200 cm

PACKED SIZE: 9 x 5 in | 22 x 13 cm

Shipping & Returns

Our warehouse is actively shipping orders from 8am to 1pm MST Monday through Friday. Most orders ship in one business day, but the transit time can take up to 7 days, depending on your distance from Boulder, Colorado.

2nd Day and Next Day Air orders will ship same day if placed by 1pm MST, Monday-Friday (except holidays).

All orders are eligible for fast and easy returns within 60 days of purchase.

For more details, please check out our Help Center

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Reactor Fleece Liner (adds up to 32°F)
Reactor Fleece Liner (adds up to 32°F)
Description || Reactor Fleece Liner (adds up to 32°F)


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 it as a 'stand alone' sleeping bag when the weather is warmer. The core THERMOLITE® fibers have the same hollow structure as a polar bear's fur, which traps a high level 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.

Design Details

Technical Features


Tech specs

  • Added Warmth
    Up to 32ºF / 18ºC
  • Best Use
    Camping, Winter Camping & Travel
  • Comes With
    Ultra-Sil stuff sack
  • Material(s)
    Thermolite fleece
  • Shape
  • Zip Options
    1/4th length zipper

Frequently Asked questions

Work as a stand-alone sleeping bag?

In many cases, yes. The only factor to be aware of is that the fleece fabric is not windproof.

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.

Work for backpacking?

It may. The Reactor Fleece is light and small enough for it to be worth carrying for the additional warmth. Weight-conscious performance users may opt for a Spark Liner or Flame Liner.