Have a Curved Back? You Need This Pack.

Most lightweight technical backpacks compensate for the different shapes of various human torsos by incorporating a degree of flexibility into their frames. That works fine if you’re only asking that pack to carry a couple dozen pounds. But the flexibility that makes them broadly comfortable also places a hard limit on the amount of weight they’re able to carry. If you need a pack capable of hauling 100 pounds or more, you need a frame that won’t flex under that load but will carry weight as close to your back as possible. And that’s a problem, because humans do not come in a uniform shape or size.

How Backpacks Work

I have a curved back. If I stand against a wall, with my heels and shoulders pressed against it, I can fit my hand between my lower back and the wall. Most of my friends have straighter backs. But if we want to go backpacking together, I can loan them one of my Osprey packs ($155 and up), safe in the knowledge that they’ll be comfortable with it, too. Osprey packs provide comfort for most people by using a mesh suspension system that holds the pack away from the wearer’s body, along with a metal wire frame that can support anywhere from 25 to 85 pounds, depending on the model. It will start to flex if the wearer really cranks down on the adjustment straps or if the pack is loaded beyond its weight rating. This works really well.

A single backpack is able to fit most people comfortably, while hauling as much weight as they likely need to to enjoy a simple camping trip. It doesn’t matter if one person’s shoulder blades poke out more than another’s, the taut mesh will simply adapt to either person’s contours, and the wire frame will compensate for any dramatic differences. But not all outdoor activities can be accomplished with a 25-to-85-pound load. The point of a backpack frame is to transfer weight vertically into the hipbelt. If that frame flexes, it begins to pull at the wearer’s shoulders, becoming uncomfortable and imbalanced. So if you need to carry a lot of weight, you need a pack frame that can support that weight without flexing at all.

This is actually something that old-school, external-frame packs excel at. A big rectangle made from tubular steel is very strong. But old external-frame packs have two inherent design flaws: (1) a big metal rectangle can’t conform to the shape of a human body, so it needs to be separated from the wearer’s back, and (2) that space means the wearer ends up carrying a hanging load several inches behind their back, pulling at their shoulders.

To really carry weight comfortably, a pack frame needs to sit flush with your back, while also being utterly inflexible. Consider the varied shapes humans come in, and I’m sure you can see the problem. Wearing weight-hauling packs designed for flatter backs than my own doesn’t just create discomfort, it also pulls my torso into an unnatural position, which can make it it difficult to breathe on steep uphills. That’s been a major issue for me, especially when I’m carrying a hundred pounds or more of meat out of the woods.

Enter Stone Glacier, a small company based in Bozeman, Montana, that’s been making packs and other high-performance hunting gear since 2012.

High-Tech Materials

By drawing resin-coated carbon fibers through a heated die under pressure, the company is able to manufacture a solid carbon-fiber stay that matches the contours of a human back. Stone Glacier employs four of those stays to in its X-Curve frame ($365), which fits curved backs like mine. (The brand’s Crux Evo frame, $365, is designed for people with straight backs.) We all know that carbon fiber is light, but few companies go through the effort of producing products from it that also take full advantage of the material’s strength. Stone Glacier has tested its backpack frames to 340 pounds with no cracking or deflection in the stays. The only thing stopping the company from finding the failure point for its packs has been the inability of a human tester to lift a heavier load onto their back. The X-Curve weighs three pounds.

Like the other, straighter frames in Stone Glacier’s lineup, the X-Curve incorporates a load shelf made from X-Pac, an extremely strong but very light laminated composite fabric. Two of the carbon stays are arranged vertically, with the other two forming an X between them; this not only facilitates proper distribution of weight vertically, down into the hipbelt, but it also prevents sideways distortion, as the load shelf carries all that weight. That shelf attaches to the frame with one-inch webbing at 12 points. It enables Stone Glacier’s frames to be used on their own, without a pack body, with any of the packs in the brand’s range, or with one of those bodies and a drybag, enabling you to move gear or meat around in a variety of ways.

I’ve been running an X-Curve paired with Stone Glacier’s Approach 1800 bag ($219). That pack only provides 31 liters of interior volume (along with a six-liter external pocket designed to accept a spotting scope). That’s not enough volume for even a quick overnighter, much less a multi-day backcountry trip, so I add a 41-liter drybag to the load shelf between the pack body and frame. The pack itself stows a couple layers and the other equipment I need during the day, while all my camping gear and food fits in the drybag. Arranged like that, I can hang the drybag in a tree at a campsite, then spend the day chasing animals around without being encumbered by an unnecessarily large or heavy pack body. Switching between the two setups takes mere seconds. Made from very strong, extremely water-repellant 500-denier Cordura, the Approach 1800 weighs 1.1 pounds.

A Custom Fit

Stone Glacier’s frames incorporate three customization features that massively aid comfort. The first are the hook-and-loop panels used to attach the shoulder straps to the frame. Seventeen percent stronger than Velcro, the material spans 24 square inches of contact area between each strap and the frame, granting each strap the ability to resist up to 400 pounds of shearing forces (which is a complicated way of saying it’s not going to come loose). It also gives you near infinite levels of adjustability when it comes to strap length and angle. In addition to my curved back, I also have a shoulder that sits lower than the other one, thanks to a motorcycle crash. The hook-and-loop connection allows me to compensate for that.

The other customization features are on the hipbelt. The lumbar pad is filled with several pieces of foam, which you can remove, reorganize, or relocate, allowing you to adjust its thickness, shape, and height. As you’d expect on a pack designed to carry an immense amount of weight, the hipbelt is also extremely burly. Two one-inch webbing straps run along each side of the belt, so it sits just above and below your pelvis’s iliac crest. The straps also allow you to adjust each side of the hipbelt individually, top and bottom, creating a perfect cradle for that protrusion’s unique shape and location on your body.

In the Mountains

During the fall, I carried this pack on two weeklong backcountry hunts and probably a dozen daylong excursions. It’s been up and down the same mountain at least 20 times and supported my load over 20 trail miles in a day in the mountains of southwest Montana. The only big game I’ve shot so far ended up being about a mile from my truck, so I just bear-hugged that mule deer for the slog out. But while I have no doubts that the X-Curve will haul an elk quarter just fine, the surprising conclusion after all that use is that I don’t think I’m going back to wearing lighter packs once hunting season is over. Stone Glacier’s pack isn’t just better at hauling loads than ultralight alternatives; that curved frame and its customization features make it more comfortable, too, even with only a couple pounds onboard.

Is this pack right for you? Unless you’re also participating in an activity like hunting that necessitates the ability to carry a hundred pounds or more, you probably don’t need to spend over $600 to achieve a setup like the one I’ve detailed here. My recommendation for Osprey’s range of packs remains unaltered, and you’ll find them plenty comfortable no matter your shape or size. But if you are a hunter, I can help you justify that expense. Not only will a secure-fitting Stone Glacier pack work during the fall, but you’ll also end up carrying it the rest of the year and for many years to come.