Swimsuits are designed to cover intimate bodily areas of men and women, subjects that have changed during different eras. Men's swimsuit styles are swimming trunks such as boardshorts, jammers, speedo-style briefs, thongs, g-strings or bikini. Women's swimsuits are generally either one-pieces, bikinis or thongs. The most recent innovation is the burqini, a more modest garment designed for Muslim women; it covers the whole body and head (but not face) in a manner similar to a diver's wetsuit.
The monokini, a style of swimsuit that most often takes the form of a bikini bottom without the corresponding top, leaves a woman's breasts uncovered. Monokinis are quite common in many places throughout South America and Europe due to the high instance of topless beaches, though due to taboos they are almost never seen in the United States, except in places with a strong European tourist influence. For pre-pubescent girls leaving the chest uncovered is sometimes considered acceptable.
Special swimsuits for competitive swimming, designed to reduce skin drag, can resemble unitards. For some kinds of swimming and diving, special bodysuits called diveskins are worn. These suits are made from spandex and provide little thermal protection, but they do protect the skin from stings and abrasion. Most competitive swimmers also wear special swimsuits including partial and full bodysuits, racerback styles, jammers and racing briefs to assist their glide through the water and gain speed advantages (see competitive swimwear).
Swimming without a bathing suit is a form of social nudity. Special nude beaches may be reserved for nude sunbathing and swimming. Swimming in the nude is also known by the slang term "skinny-dipping". As an alternative to a bathing suit, some people use their trousers, underpants or T-shirt as a make-shift swimsuit. At beaches, norms for this tend to be more relaxed than at swimming pools, which tend not to permit this because underwear is unlined, may become translucent, and may be perceived as unclean.
These are an updated version of full-body swimwear, which has been available for centuries, but complies with Islam's traditional emphasis on modest dress. They are also increasingly stylish, such as incorporating intricate sequin designs with miniskirts that go over long pants. Indonesia based ZEHBA is one of the key players in the Muslim identity apparel industry while they are increasingly popular in Turkey, Malaysia, US, Australasia and Europe.
These swim suits are created in order to make water resistance as minimal as possible and thus allowing a swimmer to move more efficiently in water. The company Speedo, for example, came out with a swimsuit called “Fastskin”. It was discovered by scientists studying sharkskin that human skin is inadequate at “slicing” the water because of its porous design. Sharkskin is made of scales spaced very closely together called dermal denticles. It is the grooves in between the scales that produce drag resistant skin. The ridges allow water to pass around the shark more efficiently. More recently, Speedo launched a new swimsuit called "Fastskin LZR RACER". Scientists carried out a global 3D body scanning exercise involving some 400 athletes to discover more about the precise shape of their bodies. Computational fluid dynamics, which can predict how existing and new product designs will behave in real-world environments, was used to evaluate the friction, pressure and fluid flow characteristics around swimmers. This analysis indicated where most drag occurs on the swimmer’s body, allowing Speedo to design for optimal drag reduction.
Some swimmers use a specialized training suit called drag suits to artificially increase drag during practice. Drag suits are swimwear with an outer layer of looser fabric - often mesh or nylon - to increase resistance against the water and build up the swimmer's endurance. They come in a variety of styles, but most resemble a looser fitting square-cut or swim brief.
In Classical antiquity swimming and bathing was most often done nude. In some settings coverings were used. Murals at Pompeii show women wearing two-piece suits covering the areas around their breasts and hips in a fashion remarkably similar to a bikini of ca. 1960. After this, the notion of special water apparel seems to have been lost for centuries.
In various cultural traditions one swims, if not in the nude, in a version in suitable material of a garment or undergarment commonly worn on land, e.g. a loincloth such as the Japanese man's fundoshi.
In the 18th century women wore "bathing gowns" in the water; these were long dresses of fabrics that would not become transparent when wet, with weights sewn into the hems so that they would not rise up in the water. The men's swim suit, a rather form-fitting wool garment with long sleeves and legs similar to long underwear, was developed and would change little for a century.
In the 19th century, the woman's two piece suit became common—the two pieces being a gown from shoulder to knees plus a set of trousers with leggings going down to the ankles.
In 1907 the swimmer Annette Kellerman from Australia visited the United States as an "underwater ballerina", a version of synchronized swimming involving diving into glass tanks. She was arrested for indecent exposure because her swimsuit showed arms, legs and the neck. Kellerman changed the suit to have long arms and legs and a collar, still keeping the close fit that revealed the shapes underneath. She later starred in several movies, including one about her life.
After this event, bathing wear started to shrink, first uncovering the arms and then the legs up to mid-thigh. Collars receded from around the neck down to around the top of the bosom. The development of new fabrics allowed for new varieties of more comfortable and practical swim wear.
Due to the figure-hugging nature of these garments, glamour photography since the 1940s and 1950s has often featured people wearing swimsuits. This subset of glamour photography eventually evolved into swimsuit photography exemplified by the Sports Illustrated annual swimsuit issues.
The first bikinis were introduced just after World War II. Early examples were not very different from the women's two pieces common since the 1920s, except that they had a gap below the breast line allowing for a section of bare midriff. They were named after Bikini Atoll, the site of several nuclear weapons tests, for their supposed explosive effect on the viewer.
Through the 1950s, it was thought proper for the lower part of the bikini to come up high enough to cover the navel. From the 1960s on, the bikini shrank in all directions until it sometimes covered little more than the nipples and genitalia, although less revealing models giving more support to the breasts remained popular. At the same time, fashion designer Rudi Gernreich introduced the monokini, a topless suit for women consisting of a modest bottom supported by two thin straps. Although not a commercial success, the suit opened eyes to new design possibilities. In the 1980s the thong or "tanga" came out of Brazil, said to have been inspired by traditional garments of native tribes in the Amazon. However, the one-piece suit continued to be popular for its more modest approach.
Men's swimsuits developed roughly in parallel to women's during this period, with the shorts covering progressively less. Eventually racing-style "speedo" suits became popular—and not just for their speed advantages. Thongs, G-strings, and bikini style suits are also worn, typically these are more popular in more tropical regions; however, they may also be worn at public swimming pools and inland lakes. But in the 1990s, longer and baggier shorts became popular, with the hems often reaching to the knees. These were often worn lower on the hips than regular shorts.