The Sea to Summit Reactor Thermolite Sleeping Bag Liner. Our best selling sleeping bag liner! The Reactor is made from 80 gram/m2 Thermolite the lightest weight Thermolite available. Thermolite is a hollow core fiber that provides extraordinary warmth for its weight and remains extremely breathable. Adds up to 14Adeg F of warmth to a sleeping bag or, used alone, is the ideal warm weather bag. Features of the Sea to Summit Reactor Thermolite Liner Lighter weight, more packable than fleece Adds up to 14Adeg F / 8Adeg C of warmth to a sleeping bag Mummy shape with a box foot Draw cord hood with mini cord lock