Used several times for mountain climbing. A waterproof dry bag that can expel air in a sealed state. The use of eVent fabric, a waterproof and breathable material, on the bottom allows for compact compression. Instead of using valves or strap tightening for compression, the opening is rolled to release air from the inside through the bottom. The oval-shaped bottom flattens to fit the internal shape of a backpack. With the eVac dry sack, you can not only protect your belongings from getting wet, but also save space.