Air valves make a compression sack bulky and hard to handle, so the geniuses at Outdoor Research came up with a better way. Instead of valves, the AirPurge Dry Compression Sack uses a section of air-permeable fabric that allows air to evacuate from the inside out without letting water from the outside in. All you have to do is fill this compression sack with gear, close it, and cinch it down until all the air escapes from inside. Your gear takes on a nice, compact form and it's protected from rain at camp or a torrential downpour on the trail.