Sea to Summit Reactor Fleece Sleeping Bag LinerThe Sea to Summit Reactor Fleece Sleeping Bag Liner is constructed using advanced hollow core Thermolite Pro fibers in a grid pattern design, making it the warmest liner option available for cold weather conditions. With added features such as shoulder zippers and a drawcord footbox, this liner gives you the ability to regulate your body temperature throughout the night. Its compatibility with the Free Flow Zip system of Sea to Summit sleeping bags