Rugged tactical polyester, Key features include: One large main compartment, one outside pocket with inside mesh accessory pockets, Hydration pocket with Velcro closure and carry handle. Complete with 2.5 liter bladder, modular attachment points on front face. Expandable design and stay-cool mesh backing. Fully adjustable shoulder straps. Heavy duty zippers and hardware. Fully expandable. 17" x 8" x 5"