In the Colter Jacket we are using patented 37.5® premium insulation, which makes you more comfortable by helping control your core temperature. The insulation retains body heat, while 37.5 active particles embedded in the insulation accelerate vapor movement and prevent overheating and moisture build-up. Strategically placed stretch panels provide freedom of movement and allow for a leaner cut. The overall result is a multi-use, comfortable, ultra-lightweight technical piece that is warm, without the bulk.