The thermolite reactor increases sleeping bag performance by up to 8 degrees celsius with 80gm2 thermalite fabric sea to summits bestselling sleeping bag liner the reactor is made from 80gm2 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 degrees celsius of warmth to a sleeping bag or can be used alone as a warm weather bag