External Frame Backpacks used to be the choice for most hikers and backpackers, until the internal frame packs appeared on the outdoor hiking equipment market. More about internal frame backpacks in the next sub-category with that name.
This type of backpack tends to be more of a rarity on the trail these days than they used to be, with their characteristic visible square frame. These backpacks are still preferred where lashing of external gear, for trail repair crews hauling their gear, or transporting game cargo for the hunter.
The design of these backpacks tend to keep the cargo containing chambers of the backpack further away from the backpackers body, potentially making the pack somewhat less stable when negotiating poorly maintained, uneven or rocky trails. Crossing of dead-fall or other such obstacles can also be more challenging to maintain a safe balance. The choice of these frames may be best suited for trails that are well maintained and graded.
Since External Frame Backpacks popularity has somewhat declined over the years, it may be more difficult to find the design and style you want, for a price you are willing to pay. You may also want to consider the relatively heavier, aluminum frame that is usually a normal component of this backpack design.While the backpack load can be readily transferred to the hip belt and provide a more comfortable upright position for walking, it also reduces the agility for the body to deal with unexpected obstacles, should rapid movement or response to a situation be needed.
Most External Frame Backpacks, except for the belt adjustment, often lack the flexibility to adjust the suspension straps, so it is therefore of greater importance to insure these backpacks are well suited to the body size of the backpacker.
The space between the these backpacks and the backpacker provides increased air flow across the back, increasing the likelihood of optimal cooling and reduction of back/backpack sweating.
These backpacks tend to be designed with a top-loading feature, and numerous smaller packets for convent access from the outside. And while lacking the smoother, more contoured lines of the Internal Frame Backpacks, still have those backpackers who will always prefer them.