, where it is known as a
Reff 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 appropriately, by transferring much of the weight to the hips and legs. Most of the weight is therefore taken off the shoulders, reducing the chance of injury from shoulder strap pressure (many backpacks equipped solely with shoulder straps can affect the posture of a person carrying more than 14 kg (30 lbs)), as well as being less restrictive of the upper body range of motion. Most backpacks can be 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.
Frameless The simplest backpack design is a bag attached to a set of shoulder straps. Such packs are used for the general transportation of goods and have variable capacity. The simplest designs consist of one main pocket. This may be 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 at night. These packs are generally produced inexpensively. Some outdoor packs, particularly those sold for day hikes,
ultralight backpacking and
mountaineering are sometimes frameless as well.
Sports 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. Running hydration packs are the smallest and lightest, many under and most under . Compression straps across the top of one's body are common, as are hip belts. Cycling hydration packs are sitting high on the back. Although daypacks are small, averaging , all trekking and hiking hydration packs are generally the largest and heaviest. and above are common.
External frame packs External frame packs were designed to carry heavy loads above , giving the wearer more support and protection and better weight distribution than a simple, frameless strapped bag. Wooden pack frames were used for centuries around the world.
Ötzi the Iceman may have used one in
Copper Age Alpine Italy, though some archaeologists believe the frame found with the body was part of a
snowshoe. Such packs are common in
military and
mountaineering applications; metal versions first appeared in the late-19th century. 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. Introduced in 1887, Merriam's innovative pack was made with drab duck canvas, which was attached to a light steel frame. In addition to two shoulder straps, the pack featured several leather straps that allowed the infantryman to attach his bedroll and canteen to the frame, instead of having them rest on his chest and hips. The most important feature, however, was 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. This system allowed the pack to elevate off the back and shoulders, and thus transfer the weight of the load onto the hips. Though he tried in vain to sell his invention to the U.S. Army, he was only able to sell a few thousand packs to the New York National Guard, and the French and Austrian Armies. Backpack design took another major leap forward with the introduction of the first aluminum external-frame backpack by Jack Abert, an avid hiker from Phoenix, Arizona. As a Boy Scout camp counselor, Abert saw firsthand how inadequate the backpacks scouts were using at that time, and set out to design a more comfortable pack. In 1947, he designed a contoured aluminum frame that was both strong and light, and shifted much of the weight off the shoulders and onto the 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. Lowe's innovation also featured the first side compression straps, the first modern sternum strap, and the first load stabilizers. Internal-frame packs have a large fabric section around an internal frame composed of strips of either aluminum, titanium, or plastic, sometimes with additional metal stays to reinforce the frame. A complex series of straps works with the frame to distribute the weight and hold it in place. 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. However, 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; 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 that do not fit inside the compartment to the outside of the pack. Internal frame packs initially 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, the improved internal frame models have largely replaced external frame backpacks for many activities. ==Daily use==