Backpacks for outdoor activities Large internal-frame backpack. One common special type of backpack (sometimes referred to as a "technical pack" or "frame pack") is designed for backpacking and other outdoors activities. These type of packs are more complex than most other backpacks. Compared to backpacks used for more day-to-day purposes such as schoolbooks, such packs are designed to carry substantially heavier loads, and as a result most such packs attach not only at the shoulders but at the hips, using a padded hip belt to distribute the majority of the weight of the pack to the legs and not the back. The often heavily padded and sometimes semi-rigid shoulder straps are mainly for balancing the weight. They usually (except for those used in ultralight backpacking) have a metal or plastic frame to support and distribute the weight of the pack. Larger packs of this type tend to have a subdivided main compartment. These trekking packs often have several pockets on the outside; they may also have lash points on the exterior (either directly attached to the frame or webbing loops), so that bulky items may be strapped on, although depending on the pack design and type of trek most backpackers will try to stuff everything into the pack. Multiday packs typically have a content between 60 and 100 liters (and are about 3ft /1 meter tall). Smaller packs with similar features are available for shorter trips.The most common materials for such packs are canvas and nylon, either ripstop fabric for lightweight packs or heavier fabric such as cordura for more typical usage. Most such packs are purpose-designed for the outdoors market; however, it is not uncommon for military surplus packing gear to be sold to outdoorspeople as well for the same purpose. The cheaper versions of the outdoor packs are often favoured by city trekkers; as they have a large volume and still carry relatively easily.
Outdoors packs, in addition to the distinction between external-frame and internal-frame, can be further subdivided based on the duration of trip a pack might be expected to be used on; daypacks hold supplies for a single day's hiking (size about 20-30 litres), while "weekender" bags can hold two to three day's worth of gear and supplies (sizes about 40-50 litres). Larger packs generally have no specific names but are designed to distribute the weight of increased numbers of gear and supplies for longer-duration trips (60-100 litres); such packs often include complex ergonomic support features to simplify the carrying of large amounts of weight. A third type with little or no frame at all, similar to the bookbags used by students and made of light fabric (often nylon ripstop, as mentioned above), is used in ultralight backpacking to eliminate the weight of the frame and heavy fabric used in more typical outdoors packs. Despite (or perhaps because of) their lesser weight, such packs are seldom less expensive than more typical, regular-weight packs.
In addition, outdoors packs are designed for specific purposes such as mountaineering, canoeing/kayaking, rock climbing, cross country skiing, and other such activities. Packs used in competitive strategic sports such as paintball and airsoft are often based on or actually are military gear.
Backpacks for professional useBackpacks are a standard part of the carrying equipment of soldiers, especially infantry, in most countries, and military-style packs are regularly available to civilians in military surplus stores. Well-known examples include the US ALICE field pack and the British Army PLCE rucksack attachment, both of which are widely available to civilian markets both as actual military surplus (new or used) and as replicas. Such packs are often, though not always, external-frame packs, with the pack itself lashed or pinned to a metal or plastic carrying frame.