The eVAC™ Dry Sack uses waterproof, air permeable eVENT® fabric on the base for valve-free air expelling, allowing compact packing. Instead of straps for compression, you just roll the sack down and air is pushed out of the base to save space and weight. The sack is oval-shaped to resist rolling when laid on their side. Suitable to keep contents dry in any wet situation where the bag is not submerged. Read more at Ask Baz.