When Wayne first began designing packs in 1977 for his newly formed company, Gregory Mountain Products, he set out to design a product that, in his own words, “must maintain its comfort and stability while effectively transferring the weight of the pack onto the hips during any activity.” At the time, Wayne was frustrated with external frame packs because he felt they did not fit the wearer properly or transfer the weight correctly, two of Gregory’s criteria for building comfortable packs to this day. In fact, Wayne’s first company, Sunbird, which pre-dated Gregory by several years, had built external frame packs (along with some early soft, or frameless, packs).
So when he started Gregory, Wayne believed that internal-frame packs were the way forward in terms of more effectively (read: comfortably) carrying weight. Wayne points to a photo he saw of mountaineer Jim Whittaker climbing around that time. Whittaker was using an external-frame pack, but he’d completely unbuckled the waistbelt - the pack didn’t have the flexibility with its rigid frame to be comfortable with the high steps you take in mountaineering and off-trail travel so he let the weight rest completely on his shoulders.
At the time, there were a few examples of what were then called ’soft packs’, or packs without the external frame structure, but these were packs that also did not have a framesheet. Wayne felt these were a better solution to the problem at hand, but unless the pack was loaded up completely (which in the process created a frame of sorts), there was basically no frame to this design, and so as soon as you began using up food and water, they too began to sag and thus did not fit correctly or transfer the weight properly.
A few years after he started Gregory, Wayne designed the Cassin which was the answer to his quest for the ultimate fit and comfort in a pack. The Cassin not only had an internal frame, but also 2 bent aluminum stays, which added stability and helped to channel the load to the lumbar area of the pack and out around the waistbelt, taking the weight off of the shoulders. The stays also allowed for more comfort, as they were bent to mimic the shape of a wearer’s back, instead of being a rigid, flat frame. In addition, Wayne used an integrated, triangle-shaped piece of fabric on the pack to attach the pack to the waistbelt stabilizer strap, which helped further channel the weight in the pack onto the hips. That design, although evolved, is still a component on Gregory packs to this day.
In essence, internal frame packs are more flexible, and when built correctly, they channel the weight in them extremely effectively to the wearer’s body. That means that internal frame packs keep the load more centered on your back during situations where the walking isn’t perfect - like rocky trails, steeper terrain, off-trail travel, mountaineering or skiing with a pack on. With Wayne’s internal frame design, he also realized the importance of a lumbar pad as a place for the weight to be channeled to and as a transfer point to move that weight out across the larger surface area of the waistbelt and onto your hips.
Frame sizes were
introduced for Gregory packs at this time as well, and Wayne was the first to figure out that your pack frame size directly correlates to your torso length, a measurement from your C7 Vertebrae to the top of your iliac crest. This ensured that if you were measured correctly for a Gregory pack, all of these suspension elements (stays, lumbar pad, harnesses and waistbelt) would sit on your body in the correct location, transfer the load to your hips properly, and so be more comfortable for carrying heavier loads for extended periods of time.
External packs are still made by many manufacturers today, and it’s just like with anything else, some people do prefer them to internal frame packs. With external frame packs, the load is being carried higher up, on the shoulders, instead of down in the lumbar area. For different body types, like someone with a larger build, this is sometimes a more preferable carry. They are also good for carrying awkward loads, such as firewood. And hunters often seek out external frame packs and remove the bag, so that they can strap quarters of big game, like elk, to the frame for more easy transport out of the backcountry.
You say tomato, I say to-mah-toe - at least we all have options.