Snuggle up with the Sea to Summit Reactor Midweight Liner, your sleeping bag's best friend. This stretchy fleece layer adds serious warmth without the bulk, and its clever design means you'll never feel trapped, whether you're a sprawler or a fidgeter. Slip it inside any bag for instant cosiness, or snap it into compatible Sea to Summit models for hassle-free layering. Lightweight, packable, and ready for whatever adventure calls.

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.

Max User Length: 170cm (Short). 185cm (Regular). 198cm (Long).

Best Use For: Backpacking, Camping & Winter Camping.

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.

Specification

• Shape: Mummy
• Added up to 6°C Warmth
• User Length: 170cm (Short). 185cm (Regular). 198cm (Long).
• Weight: 330g (Short). 350g (Regular). 355g (Long).
• Stuff sack included
• Materials: Thermolite Pro & Thermolite EcoMade