The Sea to Summit Reactor Midweight Sleeping Bag Liner is the versatile, go-to thermal boost for every adventure. Built from stretch-knit fleece with integrated armholes, it delivers exceptional freedom of movement whether you’re a side sleeper or a restless tosser-and-turner. It fits inside any sleeping bag and snaps into Sea to Summit bags for easier entry and exit.

Powered by Thermolite® Pro with Far Infrared (FIR) technology and hollow-core fibres, the Reactor Midweight efficiently traps and reflects body heat to increase warmth without unnecessary bulk—adding up to 6°C | 11°F when used as part of a sleep system.

Unlike a full sleeping bag, the liner is easy to clean and quick-drying. The HeiQ Fresh odour-control treatment helps it stay fresh during extended trips, while reducing how often you need to wash your sleeping bag—helping maintain loft and extend its usable life.

Sea to Summit Reactor Midweight Sleeping Bag Liner Features:

Freedom to Move: Stretch-knit construction and armholes allow unrestricted movement in any sleep position.
Thermal Boost: Thermolite® Pro with FIR and hollow-core fibres traps and reflects heat—adds up to 6 °C | 11 °F to your system.
Easy to Clean: Quick-drying fabric with HeiQ Fresh odour control for extended freshness on multi-day trips.
Bag Compatibility: Fits any sleeping bag and snaps into Sea to Summit bags for easier entry/exit.
Extend Bag Lifespan: Reduces need for frequent washing, maintaining insulation loft over time.
Adventure-Ready: Ideal for backpacking, hut trips, bikepacking, and travel where warmth and hygiene matter.

Sea to Summit Reactor Midweight Sleeping Bag Liner Specifications:

Added Warmth - Up to 6°C
Best Use - Backpacking, Camping & Winter Camping
Comes With - Ultra-Sil stuff sack
Material(s) - Thermolite Pro & Thermolite EcoMade
Shape - Mummy
Fits Up to Height - 185 cm
Weight - 350g

Blankets & Liners

LifeVenture Poly Cotton Sleeping Bag Liner (Rectangle)

Lifeventure Cotton Sleeping Bag Liner (Rectangle)

Sea To Summit Breeze Sleeping Bag Liner - Drawcord (Blue Atoll)

Sea to Summit Reactor Midweight Sleeping Bag Liner - Regular (Beluga)