Reactor Thermolite LinerStay extra warm during a chilly night camping under the stars. The Sea to Summit Reactor Thermolite Liner is made from a hollow core fiber that provides extraordinary warmth for its weight and remains extremely breathable. Adds up to 15 degrees F 8 degrees C of warmth to a sleeping bag or, used alone, is the ideal warm weather bag. Features: Lighter weight, more packable than fleece Adds up to 15 degrees F 8 degrees C of warmth to a sleeping bag Mummy