Editing Backpack (section)

===External frame packs===
External frame packs were designed to carry heavy loads above {{Convert|20|kg|abbr=on}}, 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,<ref name="ItalyMuseum">{{Cite web |url=http://www.iceman.it/en/the-iceman/ |title=The Iceman |publisher=South Tyrol Museum of Archaeology |date=2016 |access-date=23 July 2019 |archive-date=6 August 2019 |archive-url=https://web.archive.org/web/20190806195734/http://www.iceman.it/en/the-iceman/ |url-status=live }}</ref><ref>{{Cite web |url=http://www.primitiveways.com/pack_frame.html |title=The Three-Stick Roycroft Packframe |website=primitiveways.com |access-date=16 September 2007 |archive-date=26 January 2021 |archive-url=https://web.archive.org/web/20210126055313/http://www.primitiveways.com/pack_frame.html |url-status=live }}</ref> though some archaeologists believe the frame found with the body was part of a [[snowshoe]]. Such packs are common in [[military]] and [[mountaineering]] applications;<ref>{{Cite web |url=http://mtn.tpl.lib.wa.us/climbs/climbing/equipment/image_04.asp |title=Mountaineers |website=mtn.tpl.lib.wa.us |access-date=4 July 2007 |archive-url=https://web.archive.org/web/20131101094128/http://mtn.tpl.lib.wa.us/climbs/climbing/equipment/image_04.asp |archive-date=1 November 2013 |url-status=dead }}</ref> 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, 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. 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.<ref name="Doran-Ramble On">{{Cite book |last=Doran |first=Jeffrey J. |title=Ramble On: How Hiking Became One of the Most Popular Outdoor Activities in the World |year=2023 |publisher=Amazon Digital Services LLC - Kdp |isbn=979-8373963923}}</ref>{{rp|202-203}}

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 first-hand 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.<ref name="Doran-Ramble On" />{{rp|207-208}}

Today's external frames are typically made from aluminum, other lightweight metal alloy, and recently reinforced [[synthetic polymers]] or [[plastic]] and is equipped with a system of straps and tautly-stretched netting which prevents contact between the metal frame and user's back. In addition to comfort, this "stand-off" provides the additional benefit of creating air circulation between the frame and the wearer's back. For this reason, external frame packs are generally considered to be a "cooler load" than internal frame designs. External frame packs have a fabric "sack" portion which is usually smaller than that of internal frame packs, but have exposed frame portions above and below the sack to accommodate attachment of larger items. In addition, the sack can often be removed entirely, permitting the user to customize the configuration of their load, or to transport a non-conventional load such as a quartered game animal. Military packs are often external frame designs due to their ability to carry loads of different shapes, sizes and weights.

A recently proposed type of external frame would be made from [[Composite material|composite]] [[plastic]], which is not flexible like current backpack straps are, and can be shaped like human spine curvature. In this type of backpack, the load would directly transfer to the shoulders through the non-flexible straps, helpful in preventing damage of long term backpack carrying. This non-flexible structure also diminishes the momentum at the lumbar region of the back. The strap curvature would be shaped closely to normal spine curvature, with two flexible drawstrings to minimize backpack movement along the transverse plane. 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. This backpack type is experimental, needing further development before usage.<ref name="auto" />