The Thermolite® Reactor increases sleeping bag performance by up to 8°C with 80g/m² Thermolite® fabric. Our bestselling sleeping bag liner! The Reactor is made from 80g/ m² Thermolite®—the lightest weight Thermolite® fabric available. Thermolite® is a hollow core fibre that provides amazing warmth for its weight and remains extremely breathable. The Reactor adds up to 8°C of warmth to a sleeping bag or can be used alone as a warm weather bag.