The Rocket Pak has a very spacious and versatile 2440 Cu. In. / 40 Liters main compartment. It contains an adjustable & removable back plate and housing for a hydration system. Also another unique and versatile feature of the Rocket Pak" is it's two removable side pockets ( 915 Cu. In / 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 1830 Cu. In. / 30 Litre daypack. The Rocket Pak's back panel system is a heavily padded air permeable system for comfort and outstanding back protection. It also has contoured and heavily padded chest 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. The bottom compartment also houses a roll away waterproof cover.