The eVAC Dry Sack has a waterproof, air permeable eVENT fabric on the base for valve-free air expelling, allowing for compact packing. Instead of straps for compression, you just roll the sack down and air is pushed out of the base. Then close the buckle and you've just saved space and weight. The sack is oval-shaped, rather than round so it resists rolling when laid on its side and fits better into your pack. Suitable to keep contents dry in any wet situation where the bag is not submerged.