Sea to Summit Jet Stream Pump Sack Multiple one-way air intake ports inflate the pump quickly on the upstroke. On the down stroke, this air is expelled into the mattress through the center valve plug. Spiral stiffener prevents pump collapsing on down stroke. Made from 30D Ultra-Sil with a lightweight TPU base that has finger/thumb loops for easy grip. Roll top closure can be used as hand strap. Each stroke delivers more than a lung-full of air, without making the user dizzy or adding moisture into the mat. The Jet Stream stores small and flat, or can be used as a stuff sack for your sleeping mattress (fits most Sea to Summit air mats) or other gear. water-resistant products (such as the Ultra-Sil Stuff Sacks) are siliconized on both sides for ultimate packability waterproof products (such as the UltraSil Dry Sack are) siliconized on the outside and PU-coated on the inside to allow seam taping.