Make your sleeping bag extra warm and toasty on cold nights at the campground. The Sea to Summit Thermolite Reactor Extreme increases sleeping bag performance by up to 25 F (14 C) with super-insulating 110g/m Thermolite fabric. Thermolite is a hollow core fiber that provides extraordinary warmth for its weight and remains extremely breathable. Spacious design allows for a comfortable night's sleep, even when the mercury plummets. Perfect for extending the season of your sleeping bag.