The StackPack is the only ultralight (2.25 lbs) external frame backpack on the market. It is not designed to replace the classic external frame load hauler. The StackPack's mission is carrying 30 lbs for ultralight hiking on overnight trips, border-to-border thru-hikes, and anything in-between.
Weight is only 2lbs with two cylinders on the frame and 1 kg (36oz) with three 18" cylinders. The telescoping frame automatically adjusts to fit any torso length... no pins or clamps. Hook belt can be set for 24 to 44 inch waistline.
The bare telescoping carbon/aluminum frame weighs 12 ounces; with the shoulder straps - 16 ounces. Frame will hold from one to four gear cylinders.
Capacity with three 18x9 cylinders is 3,434 cubic inches (recommended ultralight configuration).
Capacity with four 20x10 Cylinders is 6,280 cubic inches (way beyond ultralight here).
Carry any bear canister on the bottom frame shelf (in place of bottom cylinder). Carry any heavy item on the bottom shelf (dutch oven, chainsaw, etc).