Internal-Frame vs. External-Frame Packs
A question of style, comfort, and functionality
The fight between internal frame and external frame backpacks is often considered to be a pretty one-sided battle by many outdoor enthusiasts. It seems that internal frames have most of the advantages - such as weight, stability, and maneuverability. However, even though internal frame packs are by far the most popular, there are still some people who prefer the underdog, external frame style when embarking on an outdoors trip.
Internal Frame Backpack
An internal frame backpack is popular because it uses a hidden metal (usually aluminum) or composite frame that supports the packbag from the inside. The frame is used to help place the weight on your hips, which is where your body can most effectively carry it.
Internal frame backpacks are used for all types of packs such as alpine backpacks, expedition/travel backpacks, backpacking backpacks, and so on. This is because they're ideal for mountaineering, skiing, camping, canoeing, scrambling and hiking in all types of terrain.
An internal backpack has a narrow profile, which is generally behind the shoulder harness. The frame usually consists of flat, V-shaped aluminum bars, (stays) which are about an inch wide and 1/8-inch thick. The stays give the frame some stiffness, but it still has some flexibility which allows the pack to move well with your body movements. Because these packs are slimmer you have more room to maneuver your arms for skiing and climbing, etc.
An internal frame backpack will also hold the load closer to your natural center of gravity, which is important for keeping your balance. The load is kept stable by compression straps which are used to cinch down the load and to keep individual articles bunched together. You can also adjust an internal model pretty easily as the shoulder harness and hip belt can be adjusted precisely.
An external frame backpack is designed to connect a packbag to a rigid aluminum tube frame. These types of backpacks were used almost exclusively until internal-frame designs challenged them the late 1970s. These types of backpacks are mainly used for carrying heavy loads along trails as they are quite rigid and strong. They are pretty hard to carry over rough terrain. These packs are generally heavier than internals, however lightweight models are available. External backpacks usually come with a lot of pockets for easy gear distribution and organization.
One benefit with an external model is the fact there is more open space between the frame and you back for better ventilation. You can also expand the load more easily on an external frame by attaching extra bags to the frame.
With all of the advantages of an internal frame it's probably safe to say that it's the champion of backpacks and it's pretty unlikely the external frame is going to be able to give it a serious challenge for backpacking supremacy anytime soon.