Internal or External Frames - the Debate Rages On
Americans might be interested to know that in Scandinavia, the external frame pack is more commonly used in the backcountry. Here in Canada., the internal frame pack, as well as a series of variations on that theme are the rage. In the United Kingdom (U.K.), "ramblers" carry internal frame packs almost exclusively. As usual, there are advantages and disadvantages to both designs. It's up to you to decide what's important based on your intended use, the perceived comfort of each design, and how you prefer to carry your gear.

What is an External Frame Pack?
An external frame (EF) pack is a design where the frame is fully exposed on the outside of the pack, and the pack itself is attached to the sides of the frame using straps, aluminum pins, or other methods. The frame material of choice is aluminum, mainly due to its light weight, though there are variations. The Coleman Peak 1pack frames constructed entirely of plastic, which provide a significant amount of flexibility while walking. The pack, straps, and hip belts are attached to the frame using buckles slid through holes on the frame providing a maximum amount of adjustability. Meanwhile, the basic Camp Trails frames are straight welded aluminum affairs with aluminum cross-members. Some of these designs utilize plastic separators between the cross members that allow the shoulder straps to be adjusted up or down to compensate for various torso lengths.

A basic external frame pack - the Camp Trails "McKinley". A rigid aluminum frame with a hip belt attached directly to the frame provides a basic "carrying" configuration, but little flexibility. If you're an occasional backpacker, this may be all you need.

Frames are generally slightly curved in a gentle S-shape down the sides, with cross members attaching the two sides together. Some frame designs also utilize a "lip" or shelf on the bottom, which enables the pack to stand on it's own when put on the ground and provide greater protection against unknowingly losing a sleeping bag if it's not lashed securely to the frame. The frame generally separates the pack from the back by an inch or so. Since there is ample room for air to circulate between the back and pack, EF packs are generally considered to be "cooler" to carry in warm weather, with the minor downside being that their greater distance from the back can also make them marginally harder to balance on your back.

Some frames may also include a cross member that extends beyond the top of the pack. This "extension" can be used to lash extra equipment on top of the pack, or make it easier to remove the pack from your back by providing another grab point to lift the pack off your back. The downside of the frame extension is that it can get caught on trees and branches when traveling off-trail. Even on-trail, some trail maintainers frequently forget to clear enough headroom for trail hikers, which can increase your chances of hitting branches. And during rainy or snowy conditions, branches can be weighted down. A frame extension can give you a cold or frosty shower if branches are hanging low overhead. Once again, it's a trade-off. Do you want more options to attach gear on the outside and make it easier to remove the pack, or travel "more compactly"?

What is an Internal Frame Pack?
An internal frame (IF) pack is a design where the frame is contained inside the pack. Frequently, the "frame" is nothing more than two aluminum, plastic, fiberglass, or composite "stays" that run vertically from the top to the bottom of the pack. In more advanced packs a ridget frame sheet is incorporated .They provide the primary means of support for the shoulder straps and hip belt, and some basic structure to hang the pack from.

So what is the IF pack style? An IF pack always includes a large integral compartment on the bottom for your sleeping bag. This provides greater protection from the weather (since the bag is actually inside the pack) and eliminates the chance the sleeping bag will be lost in the backcountry, or gouged/damaged while traveling through brush. In wetter locations, such as canoe trips., this is a major consideration and benefit.

There are generally fewer pockets on the outside of an IF pack, but many more lash points to attach equipment. This is likely to compensate for the loss of lash points that might have been provided by an external frame. Often, extra pockets can be purchased separately, and are often fully detachable. Many IF packs also utilize "compression straps" designed to compress the pack if it is not fully loaded. Whereas the EF pack provides a rigid frame on which to hang the pack, IF pack structure is often provided by the gear inside the pack. If the pack is not fully loaded, the compression straps eliminate the extra space by compressing the entire load into a smaller, tighter package.

Since the sleeping bag compartment is integral with the pack itself, IF packs are larger in appearance and heavier. Since the pack is carried right against the back, it is generally hotter to carry in the summer, but easier to balance. Regular users of IF packs may actually find these packs to be "over padded", and some designs allow the user to remove lumbar padding and other padding on the back. Others may find the padding an added benefit and comfort.
IF packs also carry lower on the back, which increases balance further and minimizes your chances of catching the top of the pack on branches. Manufacturers have incorporated a variety of design enhancements such as quick-wicking fabrics and "ribbed" padding designs to help in making the pack cooler to carry. And since the entire pack is carried against the back, there is a greater surface area involved in transferring weight between the pack and body. On EF packs, the weight is typically carried at only three to five points on the pack frame. With IF packs, you get a better sense that the pack is "draped" over your body - almost as if you're carrying someone on your back.

External Frame meets Flexible Body
Clearly, the greatest challenge to backpacking comfort is faced by manufacturers selling EF designs. A rigid aluminum frame locks together the opposing movements of the hips and the shoulders and minimizes the twisting action of the torso. In some cases, manufacturers have used a variety of techniques to address this incompatibility of motions, and in some cases they haven't.

Camp Trails has stuck with a straightforward design in their basic pack models. The shoulder straps are permanently attached to the horizontal cross-members near the top of the frame, and the hip belt is permanently attached to the bottom of the frame with nylon webbing and grommets. The back is separated from the frame using padded panels that can be adjusted for tautness. The frame is rigidly welded and provides no "flex". This is what I call the "basic" frame pack design, which has remained unchanged for close to thirty years. The design is perfectly adequate for carrying equipment into the back country. However, a perfectly rigid frame with permanent, non-flexible attachment points "fights" against the natural motion of the body. This design has a tendency to tire the user quicker and increases the potential for sore muscles in the shoulders and hips. If you're looking for a greater degree of comfort, you might consider some of the EF design variations.

The more refined Camp Trails models and Coleman Peak 1 packs are constructed entirely of plastic. This provides a maximum amount of flexibility in the twist motion. Depending on the attachment method for the hip belt, the amount of up and down motion (compression) possible at the hips may be limited. We've not attempted to cover all the countless design variations associated with EF packs, just provide you with a sampling.you've probably determined by now, FLEXIBILITY is the key to EF pack comfort. The more a pack moves with your natural body motion, the more comfortable it's going to be on the trail.

Internal Frame meets Flexible Body
Body motion considerations are much simpler with IF packs. Since the vertical stays are typically the only rigid part of the pack, a great deal of freedom of movement is afforded by this design. This is why you rarely (read, almost never) see someone cross-country skiing or mountaineering with an external frame pack. In most cases, the only resistance offered by an internal frame pack is by the equipment loaded inside. Often, equipment is loose enough to provide the necessary freedom of movement at all critical points on the body - at the hips, torso, and shoulders.