Granite Gear Air Vent Reduction Dryblocs (Color May Vary) Forms a block shape when compressed that stacks perfectly in your pack Simply roll to compress. Air is forced out the eVent bottom. Arched rolling stay keeps Bloc open while loading/unloading and forms an easy to grab handle when sealed XX-Small: 7 Liters, X-Small: 10 Liters, Small: 13 Liters, Medium: 18 Liters, Large: 25 Liters