Reactor Fleece Sleeping Bag Liner


SKU: 301574

Built with Thermolite® fabric and grid fleece for maximum warmth retention

The Reactor Fleece Liner built from hollow-core Thermolite® Pro fibres used in a grid-pattern to deliver our warmest sleeping bag liner and the core of any quality cold weather sleep system. You can regulate your temperature using the shoulder zippers and drawcord footbox, which also align perfectly with the Free Flow-Zip system of Sea to Summit sleeping bags. The versatile Reactor Fleece Liner delivers comfort across multiple seasons or can even be used as a stand-alone sleeping bag in warm weather. Additionally, the drawcord footbox offers plenty of ventilation and the versatility of walking around camp while still wearing your liner if needed.

BEST USE: Thermal Boost

WEIGHT: 13.8oz | 390g

LENGTH: 78in | 198cm

PACKED SIZE: 9.8 x 3.5 x 5.5in | 25 x 9 x 14cm


  • Thermal boost to retain heat and warmth, as the core of your sleep system the Reactor liner extends the performance of your sleeping bag and sleeping mat in the coldest of conditions
  • Hollow-core Thermolite® EcoMade fibres are used in a grid-pattern fleece for maximum warmth retention
  • Drawcord footbox can be opened or closed for optimal comfort and integrates perfectly with the footbox of our Free-Flow Zip system in select Sea to Summit sleeping bags
  • HeiQ Fresh odour control technology helps keep the liner fresh even after extended use
  • A mummy shape designed for maximum thermal efficiency and includes shoulder zippers and footbox drawcord for additional temperature regulation
  • Sea to Summit Guarantee is offered for the Lifetime of this product

Technical Features

HEIQ Fresh

Sea to Summit Liners are treated with HeiQ Fresh FFL, a biocide-free, highly effective odor control technology that uses a bio-based Amino Sugar Polymer to neutralize body odor. 

Thermolite Eco Made

The recycled Thermolite EcoMade fibers are made from 100% textile waste, are GRS-certified, and offer the same quality and durable lightweight warmth as their polymer virgin counterparts but with a lower carbon footprint.

Tech Specs

Comes With
Storage Case


Thermolite® EcoMade Polyester


Bio-based HeiQ Fresh Odor Control

Compact Standard
Dimensions 198 x 80 cm 216 x 80 cm
Packed Size 25 x 9 x 14 cm 25 x 9 x 14 cm
Weight 390g 420g


Does the Reactor Fleece liner have a zipper?
No - to keep weight and packed volume down, we did not include a side zipper. Snaps at the shoulders mean a wider opening than some liners for entry and exit (and the drawcord footbox allows you to vent your feet or hitch up the liner and walk around camp)

Can the Reactor Fleece liner be machine washed?
Yes. It can be washed in a machine with normal supermarket detergent - but avoid fabric softeners which reduce wicking performance. Machine dry on a cool/low setting (no dryer sheets) or air dry

How much warmth does a Reactor Fleece add to a sleeping bag?
This depends on how well your sleeping bag retains warmth (not the same as its temperature rating), how well your pad insulates (not the same as its R-Value) and a lot of other factors. You should see a significant boost if the liner is used with an appropriate sleeping bag and pad. 

How does the HEIQ-Fresh work?
The liner is impregnated with bio-based amino sugar polymers that absorb and neutralize odors. When the liner is washed, the compounds that cause odor are released, and the polymer is ready for the next use

Customer Reviews

Be the first to write a review