Sea To Summit used waterproof breathable eVent material to make the first waterproof compression bag without a valve--the eVent Compression Dry Sack. Close this Sea To Summit compression sack, and the breathable material vents air as you cinch the compression straps. No more soaked sleeping bag after a rainy day, and no more valve poking you in the back as you hike. On top of the water protection and low bulk, the eVent Compression Dry Sack weights a scant 5. 2oz (medium size).