Add warmth to your sleep system in cool or cold conditions with the Reactor Liner from Sea to Summit. Crafted with Thermolite Pro fabric featuring infrared-absorbing ceramic pigments and Thermolite EcoMade fibers, this innovative liner enhances thermal performance to the next level. The stretch-knit fabric ensures optimal comfort and a snug fit with any sleeping bag. The footbox opening provides ample ventilation and flexibility for movement around the campsite while still wearing the liner if needed. Thermal boost to retain heat and warmth: The Reactor liner acts as the core of your sleep system, enhancing the performance of your sleeping bag in colder conditions Thermolite Pro technology: Utilizes knitted, hollow-core fibers and infrared-absorbing ceramic pigments to reflect the body's heat back for enhanced warmth and comfort Offers base and shoulder openings that can be opened or closed for optimal comfort; these openings integrate seamlessly with the Free-Flow Zip system in select