Our unique proprietary Hydroknit (rtm) fabric is a true Hybrid. Hydroknit is a lamination of fleece, Lycra and breathable waterproof urethane membrane which when worn in vest form helps maintains the critical body core warmth, without bulk, while maintaining the arms free for battle. The Hydroknit vest is the perfect mid-layer for those who play hard when it gets cool. The fabric is waterproof but in this form, a vest, the seams are not sealed. Great for Sailing, Rowing/Paddling.Skiing or a walk in the woods with a freind or your favorite hound.