Osprey Stratos 40 Pack Backpanel Hydration AirCore backpanel cavity hydration option allows for versatile packing and carry options. Stratos Harness: Sewn-in spacer mesh, bungee webbing for hydration routing Straos hipbelt: Sewn-in spacer mesh with taped edges, Mesh zippered hipbelt pockets, ErgoPull closure. Stretch woven fabric front pocket provides added capacity and easy access to externals