The Sea to Summit Jet Stream Pump Sack is an efficient sleeping mattress pump, which doubles as a stuff sack. The pump works on a concertina action. Multiple one-way air intake ports inflates the pump quickly on the upstroke. On the down stroke, this air is expelled into the mattress through the centre valve plug. Each stroke delivers more than a lung-full of air, without making the user dizzy or adding moisture into the mat.