Backpack

A backpack—also called knapsack, schoolbag, rucksack, pack, booksack, bookbag, haversack, packsack, or backsack—is, in its simplest frameless form, a fabric sack carried on one's back and secured with two straps that go over the shoulders; but it can have an external or internal frame, and there are bodypacks.

[1] The name rucksack is cognate with the Danish rygsæk, Norwegian ryggsekk, Dutch rugzak, Afrikaans rugsak, Swedish ryggsäck, and Russian рюкзак (rjukzak).

Alternative names include haversack from the German Hafersack meaning "oat sack"[2] (which more properly describes a small cloth bag on a strap worn over one shoulder and originally referred to the bag of oats carried as horse fodder), Kraxe (a German rucksack with a rigid framework), and bergen (a large load-carrying rucksack, from a design issued by the British Army during the Second World War).

Most backpacks 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.

Sports and hydration backpacks are smaller with a profile closer to the body, wider straps and can come with water bladders and hip belts for running, cycling or hiking.

External frame packs were designed to carry heavy loads above 20 kg (44 lb), giving the wearer more support and protection and better weight distribution than a simple, frameless strapped bag.

The first external frame rucksack to receive a patent was made by Henry Clay Merriam, a U.S. Army officer during the late 19th century.

The most important feature, however, were the two hardwood rods that extended from the sides of the pack to leather pockets on a half-belt, which rested across the lower back and hips.

By 1950, his invention had received official approval from the National Council of the Boy Scouts of America, and by 1967, he had become the largest manufacturer of backpacking frames in the world.

A recently proposed type of external frame would be made from composite plastic, which is not flexible like current backpack straps are, and can be shaped like human spine curvature.

The straps of this backpack would be wide enough to distribute the pressure on the shoulders, with an internal white glass wool layer to absorb dynamic forces from movement.

The internal frame permits the pack to fit closely to the wearer's back and minimizes shifting of the load, which is desirable when participating in activities that involve upper-body movement such as scrambling over rocky surfaces and skiing.

The internal construction also allows for a large storage compartment; a few lash points (including webbing loops and straps for sleeping bags and other large items) may be present, but as the frame is completely integrated, it is difficult to securely lash larger and heavier items which do not fit inside the compartment to the outside of the pack.

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.

While traditionally very simple in design, school backpacks are often made with padded shoulder 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.

Because of their design, rolling backpacks reduce the strain on the user, though the shoulder straps may be used to carry the pack for short distances when the terrain is not suitable for wheels.

Backpacks are a standard part of the load-bearing equipment of soldiers, especially infantry,[13] 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.

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.

This sort of backpack is meant to safely carry knives, cooking tools, and other miscellaneous equipment such as notebooks, towels, and uniforms.