The Snugpak RocketPak has a very spacious and versatile 2,440 cubic inches/40 liters main compartment. It contains an aluminum removable stay. Removable stays can be removed and then bent to fit your back. It also has in internal pocket/sleeve for a hydration system. Also another unique and versatile feature of the RocketPak is its two removable side pockets (915 Cubic Inches / 15 Liters each) are compatible and attach to the Snugpak Yoke System. When the side pockets are attached to the Snugpak Yoke System can be made giving the user a 1,830 Cubic Inches / 30 Liter daypack. The Rocket Paks back panel system is a heavily padded air permeable system for comfort and outstanding back protection. It also has contoured and heavily padded shoulder straps faced with textured high wicking fabrics. There is a zipper compartment on the top and bottom. The top zippered compartment is a great place to store those essentials that need to be easily accessed.