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
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.
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.
Added WarmthUp to 32ºF / 18ºC
Best UseCamping, Winter Camping & Travel
Comes WithUltra-Sil stuff sack
Zip Options1/4th length zipper
Frequently Asked questions
Can you use this fleece sleeping bag liner instead of a sleeping bag?
In many cases, you can use your sleeping bag liner on its own. Keep in mind, though, that fleece fabric is not windproof and won't provide that extra protection from weather at night.
Will this sleeping bag liner add 32°F / 18°C to any sleeping bag?
Adding this sleeping bag liner won't necessarily increase the temperature inside your sleeping bag by 32°F / 18°C. There are a lot of factors involved in the thermal performance of a sleep system, starting with the insulation value of your sleeping pad.
Is this sleeping bag liner good for backpacking?
The Reactor Fleece sleeping bag liner is light and small enough to fit in your pack and could be worth carrying for the additional warmth. Weight-conscious and ultralight backpackers may opt for a Spark Liner or Flame Liner.