Back systems

Backpacks can be separated in three categories of back systems: The external frame backpack, which is the historical standard; the internal frame backpack, which came via the mountaineering world and became popular with backpackers in the 1990s, soon dominating the market for higher-end and long-distance packs; and the frameless backpack, lacking entirely the frame construction.
 

EXTERNAL FRAME

External frame backpacks are easily recognisable: the actual pack is attached to a fully visible and sturdy frame capable of carrying large loads. Shoulder straps, hip belt and sternum strap are also directly attached to the frame. The packs are easy to modify, including the option to remove the bag from its frame to vary carrying options. Most external frame packs have all kinds of places to lash extra gear on the outside, but they are usually missing separate compartments and pockets.
 

FRAMELESS

Frameless backpacks tend to be extremely light and are generally considered unsuitable for loads greater than 5-8kg or for longer outings. The lack of a frame makes load transfer to your hips inefficient resulting in most of the pack weight being carried by your shoulders. For short trips, frameless packs are a good choice if the load is minimal. Many daypacks and packs for urban use are frameless.
 

INTERNAL FRAME

Internal frame backpacks are very popular because most hikers find them more comfortable than external frame models. They are close to the body and the pack’s centre of gravity stays closer to the hiker’s own natural centre of gravity. This is especially a benefit to women, whose centre of gravity is lower than that of men. Also, the suspension system of good internal frame backpacks is highly adjustable, allowing the hiker to shift proportions of the weight to the shoulders or the hips. One of the biggest advantages is the variety of pockets and compartments on the inside and outside of internal frame backpacks, keeping the gear organized, easily accessible as well as safe and dry.

Internal frame backpacks are the smarter choice for hikers and trekkers, as they provide a level of flexibility that enhances both the hiker’s balance and comfort. The structure of an internal frame usually consists of aluminium (or other metal) stays that are fitted into sleeves within the pack. These stays contour the curvature of the hiker’s back. Frequently (as in McKinley’s advanced back systems), they can easily be fine-tuned for the perfect fit.