Folding kayaks are the descendants of ancient boats made of animal skins stretched over frames made from wood and bones, and combine modern technology with this ancient design. The earliest commercial folding kayaks were developed in the late 19th Century in Germany by Johannes Klepper, and were very popular for their compact size and ease of transport.
Like the skin-and-frame kayaks that preceeded them, modern folding kayaks are made of a flexible skin stretched over a semi-rigid skeleton. Most folding kayaks have very similar construction, even though the materials may differ. Some boats use frames made of spruce and marine plywood, while others use aluminum tubing and various plastics, and a few newer boats use carbon fiber or fiberglass composite tubing. Typically there are solid bow and stern pieces, and anywhere from three to seven ribs connected via some sort of flexible attachment to a number of longerons. Many boats follow the basic design pioneered by Klepper, whether in wood or in some synthetic material, in having a folding set of floorboards and gunwales as well as additional longerons to add stiffness and shape.
All folding boats have two-part skins, with different materials used for the deck and the hull. Decks can be made of a breathable cotton/hemp blend, as Klepper has done since their early days, or of coated synthetics, as Feathercraft, Folbot, Nautiraid and Pouch do. Each approach has its own particular benefits and drawbacks; all work well in practice. Hulls are generally made of a heavily coated synthetic fiber. In the early days, rubber coated cotton canvas was used, while the modern boats use a synthetic rubber- Hypalon, polyurethane or PVC - over a synthetic (typically Dacron) cloth.
Despite their compact size and light construction, folding kayaks can be very seaworthy. In one extreme example, Dr. Hannes Lindemann crossed the Atlantic Ocean in a 17' Klepper in 1956. Their light weight and non metallic construction has made them the choice of many military special forces.
(text adapted, with permission, from http://foldingkayaks.org)