Sea to Summit Reactor Lightweight Liner Long Overview
The Sea to Summit Reactor Lightweight Liner Long is a lightweight thermal sleeping bag liner designed to increase warmth, improve sleeping comfort and help protect your sleeping bag during backpacking, camping and hut-based adventures.
Built using stretch-knit Thermolite® Pro fabric, the liner moves naturally with your body during sleep, while integrated armholes allow greater freedom of movement compared with traditional restrictive liner designs. Using hollow-core fibre construction and Far Infrared (FIR) technology, the fabric traps and reflects body heat, increasing sleeping warmth by up to 4°C without significantly increasing pack weight or bulk.
The Reactor Lightweight Liner also helps extend the lifespan of your sleeping bag by reducing the need for frequent washing, maintaining insulation loft, and supporting long-term performance during regular outdoor use.
Quick-drying performance, HeiQ Fresh odour-control treatment, and compatibility with Sea to Summit sleeping bags make the Reactor Lightweight Liner a practical addition for travel, camping, and colder overnight conditions where additional warmth and sleeping comfort are beneficial.
Best for
- Backpacking
- Camping
- Winter camping
- Hut stays
- Travel
- Cold-weather sleep systems
- Extending sleeping bag warmth
Materials & Construction
Thermolite® Pro Fabric — Lightweight Thermal Performance
The Reactor Lightweight Liner uses Thermolite® Pro and Thermolite® EcoMade fibres designed to improve thermal efficiency while remaining lightweight and packable for backpacking use.
The hollow-core fibre construction traps warm air more effectively than standard solid fibres, helping increase insulation performance without adding excessive bulk.
FIR Technology — Heat Reflection
The Thermolite® Pro fabric incorporates Far Infrared (FIR) technology designed to reflect body heat back towards the user.
This improves thermal efficiency inside the sleep system and contributes to an added warmth increase of up to 4°C / 7°F during colder overnight conditions.
Stretch-Knit Construction — Freedom of Movement
The stretch-knit fabric construction allows the liner to move naturally with the body during sleep rather than restricting movement.
This improves sleeping comfort for side sleepers and restless sleepers while helping reduce the restrictive feeling commonly associated with traditional sleeping bag liners.
Integrated Armholes — Improved Usability
Integrated armholes provide greater freedom of movement around camp and inside the sleeping bag.
This allows easier reading, cooking, adjusting gear, or simply moving naturally without needing to fully exit the liner.
HeiQ Fresh Odour Control — Extended Trip Comfort
HeiQ Fresh odour-control treatment helps reduce odour build-up between washes.
Combined with the liner's quick-drying properties, this improves practicality during multi-day backpacking trips and travel use.
Features & Technologies
Lightweight Thermal Boost
The Reactor Lightweight Liner is designed to increase sleeping warmth by up to 4°C / 7°F while maintaining a lightweight and packable construction suitable for backpacking.
This additional warmth can help extend the temperature range of a sleeping bag during colder nights without needing to carry a heavier insulated bag.
Sleeping Bag Compatibility
The liner fits inside virtually all sleeping bags and can snap directly into compatible Sea to Summit sleeping bags for more secure positioning during sleep.
This helps prevent twisting and movement overnight while improving ease of entry and exit.
Protects Sleeping Bag Insulation
Using a liner helps reduce dirt, sweat and body oils reaching the sleeping bag insulation.
This reduces washing frequency and helps preserve insulation loft, warmth retention and long-term sleeping bag performance.
Fit & Size Guidance
Long Length Fit
The Long version is designed for users up to approximately 198 cm in height.
Its mummy-shaped profile improves thermal efficiency while still allowing comfortable movement during sleep thanks to the stretch-knit construction and integrated armholes.
Despite its increased length, the liner remains lightweight and packable for backpacking use.
Features Summary
- Thermolite® Pro insulation fabric
- FIR heat-reflective technology
- Adds up to 4°C / 7°F warmth
- Stretch-knit construction for unrestricted movement
- Integrated armholes for comfort and usability
- HeiQ Fresh odour control treatment
- Quick-drying performance
- Compatible with Sea to Summit sleeping bags
- Helps extend sleeping bag lifespan
- Lightweight mummy-shaped construction
- Includes Ultra-Sil stuff sack
Explore More Sleeping Bag Accessories
If you are building a more adaptable sleep system for backpacking, winter camping or travel, it may also be worth exploring our wider range of sleeping bag liners, sleeping mats and sleeping bags.