A backpack (also called rucksack, knapsack, packsack, pack, or Bergen) is, in its simplest form, a cloth sack carried on one's back and secured with two straps that go over the shoulders, but there can be exceptions. Light weight types of backpacks are sometimes worn on only one shoulder strap, or in the hand like an ordinary bag.

Backpacks are often preferred to handbags for carrying heavy loads, because of the limited capacity to carry heavy weights for long periods of time in the hands. Large backpacks, used to carry loads over 10 kg (22 lbs), usually offload the largest part (up to about 90%) of their weight onto padded hip belts, leaving the shoulder straps mainly for stabilising the load. This improves the potential to carry heavy loads, as the hips are stronger than the shoulders, and also increases agility and balance, since the load rides nearer the person's own center of mass.

In ancient times, the backpack was used as a means to carry the hunter's larger game and other types of prey as a way of easier transport. In the cases of larger hunts, the hunters would dismember their prey and distribute the pieces of the animal around, each one packing the meat into many wrappings and then into bags which they placed on to their backs. The bag itself was made up of different animal hide and skin (depending on what sorts of animals were in the area) and sewn together by the intestines of said animals, which were woven together tightly to make a sturdy thread-like material.

Terminology

The word backpack was coined in the United States in the 1910s. Knapsack and packsack were used before; they now occur mainly as regionalism in North America. The word rucksack is a German loanword mainly used in the UK and in the US Army: 'der Rücken' means 'the back' (the part of the body) in German. The name Rucksack is cognate with Danish Rygsæk, Norwegian Ryggsekk, Dutch Rugzak, and Swedish Ryggsäck. Alternative names include Haversack, and Bergen (from the manufacturer's name Bergens, used for a backpack supported by an external frame, usually associated with the British Armed Forces) in German language called Kraxe (in 19th century the term kraxeln was used for climbing).

Backpacks can often simply be referred to as "packs", especially in outdoors contexts; though sometimes ambiguous compared to other bags such as saddlebags and duffel bags, context is generally sufficient for identification.

A backpack fitted with pocket(s) that are suspended on the wearer's front side (chest) and loaded in such a way that the load in the front and the load in the back are about equal is called a bodypack. The majority of the load on a bodypack is carried by the hips.

The ideal load carrying system should not disturb the natural posture, balance and movement of the body. The load must be dispersed onto the skeletal structure in a balanced way. The load should not produce forces on the body in the direction fore, aft, right, or left. This body-centered load carrying system is a bodypack.

Backpack designs

Backpacks in general fall into one of four categories: frameless, external frame, internal frame, and bodypack. A pack frame, when present, serves to support the pack and distribute the weight of its contents across the body more easily (generally by transferring much of the weight to the hips and legs), so most of the weight does not rest on the shoulders, restricting range of motion and possibly causing damage from pressure on the straps. Most are capable of being closed with either a buckle mechanism, a zipper, or a dry-bag type closure though a few models use a drawstring fitted with a cord lock for the main compartment. Many backpacks with shoulder straps can affect the posture of a person carrying more than 30 pounds.

Frameless

The simplest backpack design is a bag attached to a set of shoulder straps. Such packs are used for general transportation of goods, and have variable capacity. The simplest designs consist of one main pocket. This maybe combined with webbing or cordage straps; while more sophisticated models add extra pockets, waist straps, chest straps, padded shoulder straps, padded backs, and sometimes reflective materials for added safety when the wearer is out at night. In general, these packs can be produced inexpensively.

Some outdoors packs, particularly those sold for day hikes, ultralight backpacking and mountaineering are sometimes frameless as well.

The safety of some of the designs of these backpacks have been criticized by the UK NHS, many bag designs being deemed "unsafe" for children.

External frame packs

The more traditional type of frame pack uses a rigid external frame which is strapped on the back and in turn carries and supports a cloth or leather sack and potentially strapped on items. External frames were traditionally used to carry heavy loads (20 kg / 40 lb and more), giving the wearer more support and protection and better weight distribution than a simple, frameless strapped bag. Wooden pack frames have been used for centuries around the world. Ötzi the Iceman may have used one in Copper Age Alpine Italy [27432][27433], though some archaeologists believe the frame found with the body was part of a snowshoe. Such gear was common in military and mountaineering applications right up to the 20th century [27434]; metal versions first appeared in the mid-20th century, and plastic designs towards the turn of the 21st.

Modern pack frames are usually made from lightweight metal tubes, generally aluminium but sometimes also using titanium or scandium alloys. The frame typically has a system of straps and pads to keep the sack and the frame from contacting the body. The open structure has the added benefit of improved ventilation and decreased sweatiness. The fabric part of the pack occupies part of the frame's length, but the frame typically protrudes above and below. These areas of the frame allow bulky items (such tents, sleeping bags, and thermal pads) to be strapped on. Thus the main compartment is smaller than that of an internal-frame pack, because internal space is sacrificed to allow for bulky items (tents, sleeping bags, thermal pads) to be strapped to the parts of the frame not occupied by the main compartment itself. This can result in a less smooth load and less control over the movement of the center of gravity of the pack, and can also result in bruising caused by the uncushioned frame rubbing or hitting against the body. While less popular than internal-frame gear, some manufacturers such as Kelty, Jansport, and Coleman continue to produce external packs. Military packs are often external-frame designs as well due to their increased durability.

Internal frame packs

The internal frame backpack is a recent innovation, invented in 1967 by Greg Lowe, who went on to found Lowepro, a company specializing in backpacks and other forms of carrying bags for various equipment. An internal-frame pack has a large cloth section in which a small frame is integrated. This frame generally consists of strips of either metal or plastic that mold to one's back to provide a good fit, sometimes with additional metal stays to reinforce the frame. Usually a complex series of straps works with the frame to distribute the weight and hold it in place. The close fitting of the back section to the wearer's back allows the pack to be closely attached to the body, and gives a predictable movement of the load; on the downside, the tight fit reduces ventilation, so these type of packs tend to be more sweaty than external frame packs. The internal construction also allows for a large storage compartment. Internal-frame packs may provide a few lash points (including webbing loops and straps for sleeping bags and other large items), but as the frame is fully integrated and not available on the outside, it is difficult to lash a large, heavy item so that it stays fixed and does not bounce, so most cargo must fit inside. Internal-frame packs originally suffered from smaller load capacity and less comfortable fit during steady walking, but newer models have improved greatly in these respects. In addition, because of their snug fit, they ride better in activities that involve upper-body movement such as scrambling over rocky surfaces and skiing. The improved internal frame models have largely replaced external frame backpacks for many activities.

Backpacks in daily use

In many countries, backpacks are heavily identified with students, and are a primary means of transporting educational materials to and from school. In this context they are sometimes known as bookbags or schoolbags. The purchase of a suitably fashionable, attractive, and useful backpack is a crucial back-to-school ritual for many students.

Typical school backpacks generally lack the rigid frame of an outdoor-style backpack and include only a few pockets in addition to the main holding space of the pack. While traditionally very simple in design, school backpacks are often made with padded straps and backs as well as additional reinforcement to hold large numbers of heavy textbooks, as well as safety features such as reflective panels to make the wearer of the pack more visible at night and ergonomic features such as padded straps and waist straps to distribute weight across the body. It is very common for schools (especially colleges and universities) to sell backpacks decorated with the school logo.

Backpacks are sometimes worn as fashion accessories, in which they perform the same function as a purse. Some such backpacks designed specifically for women are no larger than a typical purse, and are generally associated with younger, often college-age women.

Special-purpose backpacks

Some backpacks are specifically designed to carry certain items. Common examples include backpacks for small, high-value items such as laptops and cameras (see photo); backpacks designed to hold laptop computers in particular generally have a padded compartment to hold the computer and medium sized pockets and flaps to accomodate accessories such as charger cables and cordless/corded mice. These are especially common in college and university settings. It is also possible to buy "picnic basket" backpacks that come with plastic dishes and utensils, a tablecloth, etc. In order to supply these devices with electricity, a few high-end backpacks are equipped with solar panels.

There are also single-strap packs that are essentially a hybrid between a backpack and a messenger bag.

Inexpensive, very simple packs that combine the drawstring and straps into a single piece of cloth or webbing are occasionally sold for use at sporting events and the like. Some high-end retailers (notably Apple Stores) use a similar design for their shopping bags as well.

Rolling backpacks are backpacks with wheels on the bottom and an extending handle to ease carrying objects inside the backpacks. Because of its design, rolling backpacks reduce the strain on one's back, which is more ergonomic than regular backpacks, though some rolling backpacks can be carried on the back as well. Rolling backpacks are most commonly used to carry extensive amounts of items or moderately to very heavy items in places such as airports and international/transstate train stations.

Backpacks for professional use

Backpacks 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 United States 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 (e.g. the USMC's ILBE pack), external-frame packs, with the pack itself lashed or pinned to a metal or plastic carrying frame. For divisions that will, or will most likely, enter combat situations, packs are very heavy and can weigh an excess of 100lbs (maximum.) One should not be surprised, for each combat soldier needs to carry a part of the medical supplies, housing tents (and impromptu shelters for combat), ammunition, weaponry, and their own clothing.

Many police tactical units, as well as players of military-style combat games such as paintball and airsoft, use military-style backpacks and webbing for storing gear and ammunition. There is also a small but thriving industry devoted to creating historical reproductions of military gear; such companies generally produce period-appropriate uniforms and other gear in addition to backpacks.

Some more recent military/tactical designs, especially the MOLLE and ILBE packs used by the United States armed forces, are covered with webbing loop attachment points for increased carrying capacity.

Backpacks for leisure and travel

Backpacks are sometimes used as luggage, particularly as carry-on bags for airplane travel.

Backpacks form an essential part of the gear of the outdoor trekker and the urban backpacker, allowing more mobility and compactness than would be available to someone carrying most of their gear and clothing in a suitcase.

In addition to their use in outdoors pursuits, backpacks are sometimes used in other sports as well. Hydration packs, sometimes used by athletes and military personnel, carry water (in either a bladder or a rigid bottle) and have a tube connected to them from which the wearer can drink without removing the pack; this feature is also included in some more general-purpose hiking backpacks. Backpacks that carry skateboards have also become more popular in the youth culture.

Backpacks for outdoor activities

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 evenly distribute the weight of the pack to the legs and back for better balance and comfort (this is a must for long hikes and extensive trips through trails.) 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,(polyester), 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 kayaking/canoeing, rock climbing, mountaineering, cross country skiing, and other such activities. Hydration packs are small backpacks containing a bladder-like plastic sac to hold up to three liters of water or any other beverage for hands-free drinking; they are sometimes known as camelbacks, from the CamelBak company, the best-known manufacturer of the packs. Packs used in competitive strategic sports such as paintball and airsoft are often based on or actually are military gear.

Comparison of backpack designs

Frameless	External frame	Internal frame
Nonrigid bag strapped to shoulders	Large rigid (metal, plastic, or wood) frame to which the pack is secured	Highly reduced semirigid frame in the inside of the pack
Inexpensive and widely available	Good ventilation	Tight fit and less bouncing
Only suitable for light loads (less than about 5 kg.)	Large capacity for bulky strap-on items	Roomy internal storage, with occasional lash points for external items
~US$10–150	~US$80–200 (less popular and harder to find)	~US$100–600 (or more)/€100-600

See also

• Bindle
• Fanny pack
• Ditty bag
• Duffel bag
• Hydration pack
• Messenger bag
• Papoose
• Satchel
• Sling bag
• Shoulder straps

References