SEVEN Backpacks & Fanny packs. JOG EXPANDABLE BACKPACK - AIRPAD SYSTEM The expandable backpack with AIRPAD SYSTEM features air cushioned shoulder straps that absorb and distribute the weight in the pack. This system keeps the backpack stable while walking and adapts to different types of loads. Total capacity is 28 liters, thanks to the expandable system using the side zippers. Expandable backpack with zipper. Dimensions: Closed: 10.6 x 16.1 x 6.3 in Open: 10.6 x 16.1 x 8.7 in Capacity: 21 L closed - 28 L open. 100% Polyester