Polytetrafluoroethylene, or PTFE, is a synthetic material which can be expanded to form a porous membrane that can be laminated to fabric for its waterproof, windproof and heat resistant properties, ideal for firefighter apparel, sports and leisurewear garments and military gear.When the water vapor condenses into water droplets, the particles become larger. Due to the surface tension of the water droplets (the water molecules "pull and compete with each other"), the water molecules cannot smoothly escape from the water droplets and penetrate to the other side.