According to the volume of backpacks, backpacks can generally be divided into three categories: large, medium and small.

Large backpacks with a volume of more than 50 liters are suitable for medium and long-distance travel and more professional expeditions. For example, when you are going to a region like Tibet for a long-distance trip or a mountaineering expedition, you should undoubtedly choose a large backpack with a volume of more than 50 liters. Some short-term and medium-term trips also need a large backpack if you need to camp in the wild, because only it can hold the tents, sleeping bags and sleeping pads you need for camping. Large backpacks can be divided into mountaineering bags and long-distance travel backpacks according to different uses.

The mountaineering bag is generally long and thin, so as to pass through the narrow terrain. The bag body is divided into upper and lower layers, separated by a zipper interlayer in the middle, so that it is very convenient to take and place items. The side and top of the backpack can be tied with tents and mats, which virtually increases the volume of the backpack. There is also an ice ax set outside the backpack, which can be used for binding ice axes and snow poles. The most worth mentioning is the back structure of these backpacks. There is a light aluminum alloy inner frame to support the bag body. The shape of the back is designed according to the principle of ergonomics. "S" shape design, and there are chest straps to prevent the straps from sliding to both sides, so that the backpacker feels very comfortable. And all of these backpacks have a strong, wide and comfortable waist belt, and the height of the straps can be adjusted. The user can easily adjust the strap to a height suitable for him according to his body. Generally speaking, the bottom of the backpack is located above the hips, so that more than half of the weight of the backpack can be transferred to the waist, thereby greatly reducing the burden on the shoulders and reducing shoulder damage caused by long-term loads

The body structure of long-distance travel backpacks is similar to that of mountaineering bags, except that the body is wider and equipped with many side pockets to sort and place odds and ends. The front face of long-distance travel backpacks can usually be fully opened, making it very convenient to take and place items.
The volume of medium-sized backpacks is generally between 30 and 50 liters. These backpacks are more widely used. For 2-4 days of field trips, travel between cities and some long-distance non-camping self-help travel, medium-sized backpacks are perfect. up. It can fit your carry-on clothes and some daily necessities. The styles and types of medium-sized backpacks are more diverse. Some backpacks have added some side pockets, which are more conducive to packing items. The back structure of these packs is roughly the same as that of larger packs.
The volume of small backpacks is less than 30 liters. These backpacks are generally used in cities, and of course they are also very suitable for 1-2 days of outings.