The Sea to Summit Reactor Fleeceweight Liner provides an effective warmth boost for cold conditions while remaining lightweight, packable, and easy to care for. Made from Thermolite® Fleece, it stretches with your movements and includes armholes for unrestricted comfort—ideal for side sleepers or restless tossers. It fits inside any sleeping bag and snaps into compatible Sea to Summit bags for secure placement and effortless entry and exit. Featuring hollow-core Thermolite® fibres in a grid-fleece construction, the Fleeceweight efficiently traps and reflects body heat, increasing your sleep system’s warmth by up to 8 °C 14 °F without adding significant weight. Quick-drying and easy to clean, the liner is treated with HeiQ Fresh odour control to stay fresher on extended trips. It also helps extend your sleeping bag’s lifespan by reducing the need for frequent washing, preserving loft and long-term performance. Features Freedom to Move: Stretchable Thermolite® Fleece and armholes allow unrestricted movement in any sleep position Thermal Boost: Grid-fleece with hollow-core fibres traps and reflects heat, adding up to 8 °C 14 °F warmth Bag Compatibility: Fits any sleeping bag; snaps into Sea to Summit bags for secure placement and easy access Extend Bag Lifespan: Reduces washing frequency to maintain insulation loft and performance Easy to Clean: Quick-drying fabric with HeiQ Fresh odour control stays fresh on multi-day trips Ideal For: Cold-weather backpacking, hut trips, and winter bivvies Sizing & Weight Regular: Fits up to 185 cm Weight: 400 g