Wetsuit
A wetsuit is a garment worn to provide thermal protection while wet. It is usually made of foamed neoprene, and is worn by surfers, divers, windsurfers, canoeists, and others engaged in water sports and other activities in or on the water. Its purpose is to provide thermal insulation and protection from abrasion, ultraviolet exposure, and stings from marine organisms. It also contributes extra buoyancy. The insulation properties of neoprene foam depend mainly on bubbles of gas enclosed within the material, which reduce its ability to conduct heat. The bubbles also give the wetsuit a low density, providing buoyancy in water.
Hugh Bradner, a University of California, Berkeley, physicist, invented the modern wetsuit in 1952. Wetsuits became available in the mid-1950s and evolved as the relatively fragile foamed neoprene was first backed, and later sandwiched, with thin sheets of tougher material such as nylon or later spandex. Improvements in the way joints in the wetsuit were made by gluing, taping and blind-stitching, helped the suit to remain waterproof and reduce flushing, the replacement of water trapped between suit and body by cold water from the outside. Further improvements in the seals at the neck, wrists, ankles, and zippers produced a suit known as a "semi-dry".
Different types of wetsuit are made for different uses and for different temperatures. Suits range from a thin 2mm or less "shortie", covering just the torso, upper arm, and thighs, to thick 8mm semi-dry suit covering the torso, arms, and legs, usually complemented by neoprene boots, gloves and hood. The type of the suit depends upon the temperature of the water and the depth of the planned dive.
The difference between a wetsuit and a dry suit is that a wetsuit allows water to enter the suit, though good fit limits water circulation inside the suit, and between the inside and outside of the suit, while dry suits are designed to prevent water from entering, thus keeping the undergarments dry and preserving their insulating effectiveness. Wetsuits can give adequate protection in warm to moderately cold waters. Dry suits are typically more expensive and more complex to use, but can be used where protection from lower temperatures or contaminated water is needed.
Uses
The primary function of a wetsuit is thermal insulation to keep the wearer warm in conditions where they would otherwise lose body heat rapidly due to heat transfer by relatively large quantities of water. Secondary, and incidental, functions are buoyancy and protection from some environmental hazards such as abrasion, sunburn, and to a lesser extent, wind chill. Wetsuits are used for thermal insulation for activities where the user is likely to be immersed in water, or frequently doused with heavy spray, often approaching from near-horizontal directions, where normal wet-weather clothing is unlikely to keep the water out. Activities include underwater diving, sailing, sea rescue operations, surfing, river rafting, whitewater kayaking and in some circumstances, endurance swimming.Insulation
Still water conducts heat away from the body by pure thermal diffusion, approximately 20 to 25 times more efficiently than still air. Water has a thermal conductivity of 0.58 Wm−1K−1 while still air has a thermal conductivity of 0.024 Wm−1K−1, so an unprotected person can eventually succumb to hypothermia even in warmish water on a warm day. Wetsuits are made of closed-cell foam neoprene, a synthetic rubber that contains small bubbles of nitrogen gas when made for use as insulating material. Nitrogen, like most gases, has very low thermal conductivity compared to water or to solids, and the small and enclosed nature of the gas bubbles minimizes heat transport through the gas by convection in the same way that cloth fabrics, fur, or feathers insulate by reducing convection of enclosed air spaces. The result is that the gas-filled cavities restrict heat transfer to mostly conduction, which is partly through bubbles of entrapped gas, thereby greatly reducing heat transfer from the body to the colder water surrounding the wetsuit.Uncompressed foam neoprene has a typical thermal conductivity in the region of 0.054 Wm−1K−1, which produces about twice the heat loss of still air, or one-tenth the loss of water. However, at a depth of about of water, the thickness of a typical neoprene foam will be halved and its conductivity will be increased by about 50%, allowing heat to be lost at three times the rate at the surface. The grade of foam neoprene strongly affects insulating properties at depth, and over time. Softer, lighter, and more elastic grades contain a higher percentage of gas bubbles, and are comfortable and provide effective insulation at or near the surface where they retain much of their thickness. Areas that are significantly stretched lose thickness even before they are compressed at depth, which also reduces the insulation, and long periods under pressure and repeated compression and decompression of the neoprene foam will eventually lead to loss of volume, insulation, buoyancy and flexibility. Some bubbles will also rupture under stress and lose their gas, and the foam will start to absorb more water, further reducing insulation. Wetsuits for diving should be made from less compressible neoprene to keep their insulating qualities.
A wetsuit must have a snug fit to work efficiently when immersed; too loose a fit, particularly at the openings will allow cold water from the outside to enter when the wearer moves. Flexible seals at the suit cuffs aid in preventing heat loss in this fashion. The elasticity of the foamed neoprene and surface textiles allow enough stretch for many people to effectively wear off-the-shelf sizes, but others have to have their suits custom fitted to get a good fit that is not too tight for comfort and safety. Places where the suit bridges a hollow tend to change volume when the wearer bends that part of the body, and the change in volume of the space under the suit works as a pump to push warm water out of the suit and suck cold water in on the opposite movement.
Buoyancy
Foamed neoprene is very buoyant, helping swimmers to stay afloat, and for this reason divers need to carry extra weight based on the volume of their suit to achieve neutral buoyancy near the surface. Buoyancy is reduced by compression, and is proportional to depth and the amount of gas in the bubbles, and scuba divers can correct this by inflating the buoyancy compensator. Breath-hold divers do not have this option and have the handicap of reduced buoyancy at depth due to lung gas compression in addition to suit volume loss. The suit also loses thermal protection as the bubbles in the neoprene are compressed at depth.Measurements of volume change of neoprene foam used for wetsuits under hydrostatic compression shows that about 30% of the volume, and therefore 30% of surface buoyancy, is lost in about the first 10 m, another 30% by about 60 m, and the volume appears to stabilize at about 65% loss by about 100 m. The total buoyancy loss of a wetsuit is proportional to the initial uncompressed volume. An average person has a surface area of about 2 m2, so the uncompressed volume of a full one piece 6 mm thick wetsuit will be in the order of 1.75 x 0.006 = 0.0105 m3, or roughly 10 liters. The mass will depend on the specific formulation of the foam, but will probably be in the order of 4 kg, for a net buoyancy of about 6 kg at the surface. Depending on the overall buoyancy of the diver, this will generally require 6 kg of additional weight to bring the diver to neutral buoyancy to allow reasonably easy descent. The volume lost at 10 m is about 3 liters, or 3 kg of buoyancy, rising to about 6 kg buoyancy lost at about 60 m. This could nearly double for a large person wearing a farmer-john and jacket for cold water. This loss of buoyancy must be balanced by inflating the buoyancy compensator to maintain neutral buoyancy at depth.
There is also a buoyancy loss due to gas loss from the bubbles over time, and the neoprene also loses flexibility with time, and tends to stiffen and shrink. This tendency is exacerbated by frequent use, deep dives, and exposure to sunlight. The "compressed" or "crushed" neoprene used for hot water suits and dry suits is permanently reduced in volume by intentional hydrostatic compression during the manufacturing process, specifically to reduce buoyancy change with depth, at the cost of reducing insulation.
History
Origins
In 1952, UC Berkeley and subsequent UC San Diego SIO physicist Hugh Bradner, who is considered to be the original inventor and "father of the modern wetsuit," had the insight that a thin layer of trapped water could be tolerated between the suit fabric and the skin, so long as sufficient insulation was present in the fabric of the suit. In this case, the water would quickly reach skin temperature and gas bubbles in the fabric would continue to act as the thermal insulation to keep it that way. In the popular mind, the layer of water between skin and suit has been credited with providing the insulation, but Bradner clearly understood that the suit did not need to be wet because it was not the water that provided the insulation but rather the gas in the suit fabric. He initially sent his ideas to Lauriston C. "Larry" Marshall who was involved in a U.S. Navy/National Research Council Panel on Underwater Swimmers. However, it was Willard Bascom, an engineer at the Scripps Institution of Oceanography in La Jolla, California, who suggested foamed neoprene as a feasible material to Bradner.Bradner and Bascom were not overly interested in profiting from their design and were unable to successfully market a version to the public. They attempted to patent their neoprene wetsuit design, but their application was rejected because the design was viewed as too similar to a flight suit. The United States Navy also turned down Bradner's and Bascom's offer to supply its swimmers and frogmen with the new wetsuits due to concerns that the gas in the neoprene component of the suits might make it easier for naval divers to be detected by underwater sonar. The first written documentation of Bradner's invention was in a letter to Marshall, dated June 21, 1951.
Jack O'Neill started using closed-cell neoprene foam which he claimed was shown to him by his bodysurfing friend, Harry Hind, who knew of it as an insulating material in his laboratory work. After experimenting with the material and finding it superior to other insulating foams, O'Neill founded the successful wetsuit manufacturing company called O'Neill in a San Francisco garage in 1952, later relocating to Santa Cruz, California in 1959 with the motto "It's Always Summer on the Inside". Bob and Bill Meistrell, from Manhattan Beach, California, also started experimenting with neoprene around 1953. They started a company which would later be named Body Glove.
Neoprene was not the only material used in early wetsuits, particularly in Europe and Australia. The Pêche-Sport "isothermic" suit invented by Georges Beuchat in 1953 and the UK-made Siebe Gorman Swimsuit were both made out of sponge rubber. The Heinke Dolphin Suit of the same period, also made in England, came in a green male and a white female version, both manufactured from natural rubber lined with stockinet. As early as July 1951, underwater hunters in Australia were experimenting with a natural rubber wetsuit "of a 'wrap on' variety, which does not set out to be 100% waterproof the leakage of water through it is so slow that body warmth under it is maintained for hours." By May 1953, the Bondi underwater equipment manufacturer Undersee Products was already distributing this singlet-like design commercially to Australian sporting goods stores, where it was described thus: "Made from heavy sheet rubber, the Sealskin suit is most effective when worn over a football jersey. When jersey becomes wet, rubber holds it firmly against body and thus warmth is generated. Water circulation automatically stops and body warmth builds up in moisture-laden jersey. The Seaskin suit provides both underwater insulation and above-water wind protection".