Premium Thermal Performance for Extreme Cold and Solo Travel

The Sea to Summit Reactor Fleeceweight Liner is the warmest model in the Reactor series, engineered for adventurers who need a significant thermal boost for their sleep system or a lightweight standalone bag for warm-weather trips. Constructed from Thermolite® grid fleece, this liner uses hollow-core fibers that trap an incredible amount of air to provide superior insulation without the bulk. The specialized grid pattern not only enhances warmth by reflecting body heat but also provides a soft, "brushed" texture against the skin, making it a luxurious upgrade for any sleeping bag.

To ensure every adventurer finds their ideal fit, we carry the Reactor Fleeceweight in two distinct sizes. The Regular size offers a streamlined, thermally efficient fit for most users, while the Long model provides extra length for taller campers, ensuring complete coverage and preventing cold spots at the feet or hood. Both sizes feature a technical mummy shape with a drawcord hood to lock in heat and a boxed foot for ample wiggle room. Treated with HeiQ Fresh for long-term odor control, this liner is the perfect companion for extending your 3-season bag into the winter months.

Key Features:

• Extreme Warmth Boost: Adds up to 18°C (32°F) of warmth to your sleeping bag, significantly extending its seasonal range.
• Available in Two Sizes: Choose between Regular (for standard heights) and Long (for taller users) for a personalized fit.
• Thermolite® Grid Fleece: High-loft, hollow-core fibers provide exceptional warmth and moisture-wicking capabilities.
• Standalone Versatility: Can be used as a standalone ultra-lightweight bag in tropical or warm-summer conditions.
• Mummy-Shaped Design: Features a tapered foot and a drawcord hood to maximize heat retention and minimize weight.
• HeiQ Fresh Odor Control: Biocide-free fabric treatment helps keep the liner fresh during extended backcountry expeditions.
• Quick-Drying Fabric: Easy to wash and dries significantly faster than traditional cotton or fleece liners.
• Compact Stuff Sack: Includes a lightweight storage bag for easy transport in any backpack or bikepacking setup.