Named for its advanced temperature management technology. H2Flow mechanical venting has a series of perforations, air pockets, and vents that let air flow freely. The air pockets in the fleece lining trap body heat to keep you warm. If things get too hot, crank open the vents, let that trapped warm air free and get cool air circulating. The jacket is a warm mid-layer or a lightweight outer jacket, depending upon weather. Material: Fleece, Polyester.