Unfortunately, its not always warm when we are out there...but you still go...which is why we created the Essential Belay Jacket. Light and compressible for the warmth retained this jacket on materials and construction techniques to do the job for you. Two layers of Ramtect compressed wool is sandwhiched in-between the lightweight and windproof outer shell and the inner lining. All told this creates 5 layers of dead air space compared to three layers if you use a single layer of insulation. Dead air space traps warmth leaving you MUCH happier on those colder days. Trust the Essential Belay Jacket to keep you comfortable.