A Sub-One Pound Ultralight Framed Backpack

Solving the mystery of bending 7075 aluminum tube to make an ultralight backpack frame.

Suspension Design

This was the real design challenge. My goal was obviously to make the lightest frame possible for loads with a total weight of around 25 pounds or less. The simplest and way to accomplish this would be to just add two vertical frame stays on the outside edge of the back panel – somewhat similar to how KS Ultralight does their frame stays. These can be super light, if you use carbon possibly less than an ounce for the pair.

This simple design can work ok on fairly light loads, but it has a couple serious drawbacks I wanted to avoid. First is there is zero lateral rigidity, and second is the straight stays don’t fit the curves of a human lumbar at all. In my case, I’ve tried them on a couple other packs, and they would often hit my shoulder blades at right around the shoulder strap. This isn’t always an issue, especially on packs that tend to barrel when they are stuffed because it pushes the stays away from the back. In general, I’d like to avoid barreling as much as possible and keep the load as close to my body as possible. The frame does help quite a bit in this regard, and the side panels being cut to match the curve of the stays gives it additional shape and structure when fully loaded.

There is, however, one really big advantage to moving the frame to the periphery of the back panel, and that is you don’t need much if any padding to keep the stays from hitting your back if they are curved correctly. With a good curve the frame itself never contacts any part of your body, leaving just a well packed bag for the padding. That’s the single biggest thing you can do to save weight on a framed pack – get rid of the unnecessary padding.

The frame is also a little different than lots of ultralight setups because it is on the exterior of the pack, not the interior. This allows the frame stays to terminate directly into the hip belt wings via a 500d Cordura pocket, instead of having a few layers of fabric between the frame and the hip belt. This eliminates a lot of fabric twisting, stretch and collapse that can affect very light packs when the total pack weight gets above 20 or 25 pounds. This exterior approach means it also takes very little additional fabric weight to hold the frame in place, as the grosgrain for the compression cords do double duty. The top of the frame is held in place by two pockets that capture the right angles of the stays, and stretch over the frame to hold it in place.

Without a doubt, the most difficult part of this process was bending the actual frame. I went with 7075 Aluminum, which is incredibly light and strong. The drawback is it is very hard to bend without breaking, or at the very least kinking. 6061 is a much better option when it comes to bending, but it comes with at least a 50 percent weight penalty.

I spent a couple months on and off trying different technique to bend the 7075 tubing, before I finally built a jig I could roll the tubing along and into the correct shapes. Putting one large radius curve in the tubing proved to be fairly easy, the difficult part was putting two smaller radius curves on a single tube to make the “s.” I’m pretty stoked about the results, and after building the jig I am super happy with the results. The results are good enough I also bent custom stays to replace the frames in other packs I already own, which you can read about here.

This is actually the second build I’ve done with the exact same frameset and nearly identical pattern. The first pack came in at nearly 23 ounces, despite very similar volume and frameset, but it had burlier fabric choices and a small zippered panel on the front to allow a camera insert to be used. Here is where the rest of the weight is saved.

Hipbelt
Panel loader: modular full wrap-around 3/8 EVA foam hipbelt and a double pull 1 inch buckle.
Ultralight: Wings with no lumbar pad, 1/4 inch EVA foam. 1 1/2 inch single pull buckle.

Loadlifters
Panel Loader: 3/4 inch webbing and ladder locks
Ultralight: 1.2mm Spectra line and Lineloc tensioners

Suspension
Panel Loader: Entire frame is held in place by 500d cordura channels and reinforcements.
Ultralight: Frame is held by 1/2 inch grosgrain loops and 500d Cordura pockets.

Fabric choices
Panel Loader: HyperD 300 body panels, 500D cordura pockets, front and bottom panel. Outer pocket is spandura.
Ultralight: 100D Robic Nylon main body, 210D Robic pockets and bottom panel. Outer pocket is polyester utility netting.

Top Closure
Panel Loader: Lunch bag style closure with Kam Snaps and a small roll-top
Ultralight: Drawstring closure with 1.0 mm UHMPWE cord. (A drawstring is the lightest and most fabric efficient closure.)

Things I’ll Change for v3

I need to find different fold over elastic. The large holes in the polyester utility netting are very difficult to capture with a zig zag stitch in the elastic. I think a wider elastic will give a better margin for error.

I like the 210 denier bottom panel to wrap up onto the main panel a few inches for extra durability, and I’ll probably move it at least another inch higher still. This just keeps the netting from snagging on debris when you put your pack down, and keep it from ripping.

The other major flaw is the side pocket design – it’s simply not a big enough opening. This current version will work ok, but When the pack is fully loaded, it tends to stretch the pack and because the pockets are already pretty tight, sliding a water bottle into the pocket is a little harder than it needs to be. Another inch or two on the opening would be ideal.