Material:Polyester. YKK Zipper and YKK Buckle The main compartment is the size of the whole backpack. Mine is 20"h x 12"w x 4.5" deep.Your Laptop(big enough for a 17"laptop).There is a compartment that can be used for a bladder and a holding place for the tube but no specific bladder space. The size is perfect and meets the personal carry on for airlines such as frontier so you can load these down and not pay for a checked bag.
The belly strap is not removable, but it can be strapped to the pack itself to keep the pack fairly flush against your back without using the strap.(the size:25--53 inches) Use the waist belt, and slightly loosen the shoulder straps to shift the weight to the hips. That is what the hip belt on all backpacks is for. Adjust until comfortable. Also, use the sternum strap. It will bring the shoulder straps in tighter to the chest. It will also help prevent the shoulder straps from falling off the shoulders.