As debates go this one is mild, absent of the heated rhetoric you sometimes encounter when folks become heavily biased in one direction or another. Perhaps it’s because there is no clear-cut answer-it simply depends on personal preference and the sort of trip you have in mind.
Walk around with a pack on your back and you are going to generate heat. And the heavier the load or the more aggressive the trail the more you’re going to generate. In the cold weather, it’s nice to retain that heat so you stay warm. But if you are out hiking in sweltering summer sun you prefer to send heat away from you. An internal frame pack snugs up against your body whereas the external frame puts some space between you and the pack, allowing heat to escape more readily. read this guide
External frame packs have an edge when it comes to strength. So if you have a lot of weight to carry, the rigidity of an external frame pack with its ability to handle a good amount of weight may prove attractive. On the other hand, the closer the load is to your body the more comfortable it is to carry. Internal frame backpacks let you position the load as close to your body as possible.
It’s interesting to note that internal frame packs are the most popular. The hidden frames of aluminum or composite material give structure to the pack from the inside and help position the load so you carry the bulk of the weight on your hips-the best place to carry it. Internal frame packs also have a slimmer profile, affording the wearer increased maneuverability-a real plus when it comes to skiing and climbing. Balance, too, is helped by an internal frame pack as the load is positioned closer to your center of gravity.