The Crater Lake is quickly becoming one of our most popular rectangle bags. It uses 2-layer offset construction to eliminate cold spots. It is composed of Techloft+ Insulation. Techloft+ Insulation consists of multi-hole staple-length micro-denier fibers that have a siliconized finish for maximum insulation, loft,and compactness. This sleeping bag series is great for camping when weather conditions are cold and you want to stay warm.