Go by any school yard and the majority of students will have a typical lightweight daypack. Unlike external or internal frame backpacks, daypacks do not usually have any frame at all. They are the smallest of the backpack types and the least expensive. Daypacks, as their name suggests, are designed for a recreational hike or simple duties. Daypacks are perfect for carrying books, school supplies, and maybe a small lunch bag. When hiking with a daypack, you can usually fit a sweater or jacket, a limited amount of gear and enough food for a day trip in good weather. In a pinch, you could probably use a daypack for an overnight trip, but it would take some clever packing and nice weather. You would not have room for rain gear.
External frame backpacks are exactly what their name implies. They are large and have a lightweight frame, usually metal, surrounding them. Different than the internal frame backpacks that require all items to be carried inside the pack, the external frame pack allows you to hang things from the frame. Although tying things to the frame can save space in the pack, it can also be a disadvantage in certain situations, like climbing. The external frame backpack is designed for the serious hiker and works well on terrain that is not hilly or demanding. These backpacks are also uncomfortable. They are awkward and bulky, and do not fit well against your body. Although these backpacks are great for carrying a lot of gear, they just don’t measure up when it comes to comfort.
It has been said that necessity is the mother of invention. This certainly holds true for the creation of internal frame backpacks. Basically, internal frame backpacks were designed to overcome all the undesirable features associated with the external frame backpacks. There are a few attributes that give this backpack a big edge over the external frame model. Internal frame backpacks are constructed with the frame on the inside of the pack. This frame is flexible and allows the backpack to fit the contour of your body resulting in a much more comfortable fit. Internal frame backpacks are also wider at the bottom. This feature lowers the center of gravity making it much easier to balance. You do not have the outer frame to hang things on, but depending on your needs this can be a good thing or a disadvantage. The fact that everything has to be carried inside internal frame backpacks is a plus when you want to avoid sagging or wet snow. You also do not want anything hanging off your pack when you are doing any off trail hiking or climbing.
When searching for external frame or internal frame backpacks, it is important to look for all the features you will need. Remember comfort and weight , and be sure to look for plenty of padding. Other features that should be present in a well built pack are curved shoulder pads, hip belts, a back that breathes, and adjustable suspension.