Made with 37.5 technology, these signature suit separates pants features fabric that is triggered by your body temperature to either warm or cool you depending on the situation. The active particles permanently embedded in the yarn capture heat from your body's infrared energy to speed evaporation and cool you if there is moisture vapor (sweat) present, or retain that heat to keep you warm when no moisture is present. With suit separates, you get to choose jacket, pant, and vest sizes separately for a custom fit.