I bought a slightly used Kelty large daypack. It looked almost unused, except for a broken zipper slide. I would guess it was around 3200 ci. The internal frame consisted of two aluminum stays, each about 3/4"*1/8" in cross section. I took it on an easy backpack (2 or 3 miles on a fire-road in each direction). I strapped on a backpacking version of a Coleman stove, which was about 1 foot * 2 feet * 4 inches, and weighing about 5 pounds. I strapped it to some daisy chains (aka bartacked webbing) on the outside of the backpack. I made the straps tight enough so the stove wouldn't fall off. After the backpack I noticed that several of the bartacks had failed. This was quite unexpected. It is possible that some seam also blew out. I was unimpressed that the bartacks blew out. Obviously of inferior construction. I sent it back to Kelty for repair, and sold it when I got it back. Not recommended.
Around 1990 I bought a MontBell backpack at their store in northern California. I was interested in their packs, since they made the legendary Chounard Zero Point pack, which was very big and very light. The pack I got was about 5000 ci and was supposedly made of tensilite, a special nylon from Japan that was very strong, and very abrasion resistant. The internal frame consisted of two pieces of hollow, plastic, with internal plastic ribs, and a cross section of about 2"*1/8". Each rib had a metal rod at each edge, for a total of 4 metal rods. The pack was not very comfortable, nor very supportive. It didn't look like a well designed or well built pack. I loaded it up for a easy backpack in Joshua Tree. The day of the backpack found me in a campground in Joshua Tree. I dragged the loaded pack about a foot in the degenerate granite gravel, so common there, and wore two holes through the pack. After the backpack, I called MontBell, and they explained that I got a demo pack (which I knew). They also explained that the demo pack had the same weight nylon as the real pack, but wasn't the elusive tensilite, but rather common nylon. Being very light weight nylon, it simply wore through. Since we had a misunderstanding about what 'demo' meant when I bought the pack, I sent it back. Not recommended.
I bought a The North Face Snow Leopard II (large). This is a large internal frame pack. I would guess it is about 5500 ci. I used it on a 3 day backpack. It seemed to be reasonably made (much, much better than the MontBell), but I did not find it very comfortable. I suspect that the regular sized pack might have fit me better. I am 5'11", but I think the pack was designed more for someone at least 6'3". I sold it for a modest profit.
I bought a factory second large external frame REI backpack. I would guess it was about 3500 ci. It was only $40 (around 1986). About the second time I used it, some sewing holding some webbing failed. I sewed it back together, and it has been fine ever since. The sternum strap webbing also failed shortly thereafter, and I fixed it also. It is a reasonable pack, though the quality control used in its construction is unimpressive.
An external frame backpack. Very light and very unconventional design. It uses thin wall large diameter aluminum tubing for the frame. For the hipbelt, there are pivoting arms of aluminum that come out from the frame to support the hipbelt. There are no shoulder straps, rather there is a wide mesh fabric that has roughly twice the surface area of conventional shoulder straps. This distributes the weight very well over the surface of the chest, and is very light. The pack itself consists of many zippered compartments, generally rectangular shaped. There is room above the pack for a large sleeping bag or sleeping bag and tent.
I used it two or three times. High quality design and construction. Not sure if the design is correct or not. The jury is still out. Not in production anymore.
Jack has some unusual ideas about quality control and customer service. Here are some letters between him and me, that should be read before anyone considers buying his products.
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