Warm, dry and soft are the tenets of Primaloft brand insulation. Oringinally developed for the military in the 80's, this insulating material has becom widely known through military and civilian circles as being durable and dependable. The insulation itself is made up of utra-fine fibers that use their extensive surface area and tight weave to trap warm air. The synthetic nature and treated coatings of these fibers also make them water resistant, allowing the garments they are used in to maintain their warmth, even when wet. This gives Primaloft and other synthetics an advantage over down, which loses its insulating capabilities when wet. Primaloft is also extremely compressible, making it great for layers, or when packing insulated jackets and pants for a trip.