Backpacks come in all shapes and sizes with basically two different types for the backcountry packer.read more
1) Internal frame backpack
2) External frame backpack
So which is best and why? Well the short answer is it depends. It will depend on how heavy a load you plan on carrying, type of terrain expected, your activity while carrying the pack, how much stuff you plan on packing, is the weather hot or cold, and finally which fits your style best.
External frame backpacks have the framework on the outside. These “old-school-style” packs can carry more weight while positioning the weight higher on your back. This allows for good vertical load transfers to the hips providing you with a more natural upright walking posture. They are very suitable to hiking on well established trails without low over-hanging branches or difficult terrain. The frame also keeps the pack suspended away from your back allowing lots of air flow between you and your pack making it cooler to use in hot weather. The external frame provides for easy attachment of extra gear. Proper loading is accomplished more easily with the many small compartments and the framework allows the wearer to carry awkward unbalanced loads easily.
The downsides to externals are that they do carry the weight high and away from your back so they don’t have the best stability. You run the risk of feeling tipsy and off-balanced during scrambling maneuvers or when climbing or descending dicey terrain. These packs often tend to be wider and bulky sticking out from your body, so they tend to get hung up on branches and brush in close quarters.
Internal frame backpacks have the framework on the inside the pack. This makes for a much more compact and form-fitting pack, better for the backpacker who’ll be hiking rugged trails that require freedom of movement and balance, or activities that require independent arm movement (skiing, climbing, etc). The flexible suspension can be formed to follow the contours of the spine. The load also rides close to the back and brings the pack’s center of gravity closer to the wearer’s center of gravity, creating a balanced and stable load during higher speed activities.
The downsides to internals are that they usually have one big center compartment rather than many small compartments making it more difficult to load and find gear. There are not as many options available to hang extra gear on the outside of the pack because the frame is not exposed. With an internal frame you can have a tendency to walk leaning forward to counterbalance the load on your back. Also they are much hotter on your back because they don’t allow air flow between your pack and back.