A swimsuit is an article of clothing designed to be worn by people engaging in a water-based activity or water sports, such as swimming, diving and surfing, or sun-orientated activities, such as sun bathing. Different types and styles may be worn by men, women, and children. Swimsuits can be described by various names, some of which are used only in particular locations or for particular types of suit, including swimwear, bathing suit, bathing attire, swimming costume, bathing costume, swimming suit, swimmers, swimming togs, bathers, cossie (short for "costume"), or swimming trunks (swimwear that resembles shorts), besides others.

A swimsuit can be worn as an undergarment in sports that sometimes require a wetsuit or drysuit such as cold water swimming, water skiing, scuba diving, surfing, and wakeboarding. Swimsuits may also be worn to display the wearer's physical attributes, as in the case of beauty pageants or bodybuilding contests, and glamour photography and magazines like the annual Sports Illustrated Swimsuit Issue featuring models and sports personalities in swimsuits.

There is a very wide range of styles of modern swimsuits available, which vary as to body coverage and materials. The choice of style may depend on community standards of modesty, as well as current fashions, and personal preferences. The choice will also consider the occasion, for example whether it is to be worn for a passive occasion such as sunbathing or for an activity such as surfing or swimsuit competition. Swimwear universally covers at least the wearer's crotch area. According to international standards for social etiquette and swimming functionality, male swimwear usually leaves the upper body uncovered, while swimsuits for girls and women usually cover the chest or at least the nipples.

Materials Prior to the 1930s, swimsuits were typically made of wool; however, such suits did not hug the body and became heavy with water.

Rayon began to be used in the 1920s in the manufacture of tight-fitting swimsuits, but its durability, especially when wet, proved problematic, with jersey and silk also sometimes being used.

In the 1930s, new materials were being developed and used in swimwear, particularly latex and nylon. Swimsuits incorporating nylon dry more quickly than swimsuits made of common organic fibers, which can create a more comfortable experience for the wearer. Swimsuits gradually began hugging the body, especially women's swimsuits.

In the 1960s, spandex (Lycra) began to be used in swimsuits, usually combined with nylon, to make them fit snugly to the body. However, spandex is not particularly strong or durable, especially in chlorinated water in swimming pools and hot tubs.

Polyester is becoming more common as a durable, lightweight fabric for swimsuits, although it is not as stretchy as spandex.

Some companies have started to focus on recycled materials for their swimwear. They are working with companies that transform fishnets, nylon waste, and recovered plastic from shorelines, waterways and coastal communities into textile components.

Swimsuit styles

In Western culture, men's swimsuit styles include boardshorts, jammers, swim trunks, briefs (also known as "Speedos"), thongs, and g-strings, in order of decreasing lower body coverage, and women's swimsuits include one-piece, bikinis, or thongs. While they go through many trends in color, pattern, length, and cut, there is not much modification to the original variety of suit.

A recent innovation is the burkini, favored by some Muslim women, which covers the whole body and head (but not face) in a manner similar to a diver's wetsuit. These are an updated version of full-body swimwear, which has been available for centuries, but conforms with Islam's traditional emphasis on modest dress. In Egypt, the term "Sharia swimsuit" is used to describe full-body swimwear.

Swimsuit color affects swimmers' safety. A blue, white, or gray swimsuit may be nearly invisible when the swimmer is underwater, which can make it more difficult for a lifeguard to spot a drowning swimmer. The most visible swimsuits underwater have large, solid blocks of bright neon colors, such as neon pink or neon orange. Solid neon colors are more visible than red or multi-colored swimsuits.

Unisex styles Name Image Description Drag suits A drag suit is a pair of baggy square-cut or brief-style trunks that competitive swimmers may wear over their normal suit to provide extra resistance ("drag") from the water. This allows the swimmer to get more out of their training than they would without a drag suit. Dry suits A dry suit or drysuit provides the wearer with environmental protection by way of thermal insulation and exclusion of water, and is worn by divers, boaters, water sports enthusiasts, and others who work or play in or near cold or contaminated water. A dry suit normally protects the whole body except the head, hands, and possibly the feet. In hazmat configurations, however, all of these are covered as well. Racing suits Swimsuits made of technologically advanced fabrics biomimetically designed with a surface that mimics the rough shark denticles to reduce drag along with key areas of the body . The characteristics of the fabric improve shape retention and increase muscle compression to reduce vibration and retain muscle shape to reduce fatigue and power loss. Available in a variety of cuts such as bodyskin, legskin, high cut swim briefs, and kneeskin. Rash guard(also known as rash vest or rashie) A type of athletic shirt made of spandex and nylon or polyester, used to protect against rashes from abrasion (like wax-based chafing from sliding on and off of a surf board) or sun exposure. Rash guards may be worn as an alternative to wetsuits during warmer weather. They may also offer UV protection. Sling swimsuit The sling swimsuit is a one-piece swimsuit which is supported by fabric at the neck. The sling swimsuit is also known by a variety of names including "suspender bikini", "sling bikini", "slingkini", "suspender thong", "slingshot swimsuit" or just "slingshot". It is so named because of its resemblance to the Y-shape frame of a slingshot. It is sometimes listed as a bikini variant. Monokini types also exist. When designed for or worn by a man, it is often called a "mankini". The image to the left is of a man wearing a green mankini, a swimsuit made famous by the 2006 film Borat.Swim shirtA more comfortable and casually worn athletic shirt that protects against sun exposure and chafing. It is often used as a simple alternative to sunscreen while swimming to prevent possible skin cancer, and many swim shirts have a UPF rating of 50+ for this purpose. Wetsuits Wetsuits are insulated, close-fitting suits designed for prolonged immersion, usually in the context of snorkeling, scuba diving, or surfing, and other water boardsports. Made from neoprene, they come in different thicknesses and styles. Wetsuits keep the wearer warm by trapping a thin layer of water close to the skin which heats up due to body temperature.

Women's swimsuits Name Image Description Bikini(also known as a two-piece) One piece covers the breasts, and the other the crotch, leaving an uncovered area between the two. Bikinis are available in many stylistic variations. Burkini (also called burqini) Two piece that covers the whole body except feet and hands, and which may have a hood to cover the head (but not face), made of ordinary swimsuit fabric, in a shape similar to a diver's wetsuit. Although sometimes labeled as a religious garment, it is also worn for health reasons by lifeguards and other women who are high risk for skin cancer, or who do not feel comfortable wearing skimpier alternatives. The burqini was originally designed in Australia by Aheda Zanetti. Her company Ahiida owns the trademarks to the words burkini and burqini, but they are sometimes used as generic terms for similar forms of swimwear. Attempts to ban burqinis in France for being too religious led to significantly increased sales worldwide. Monokini The monokini, also known as a "topless bikini" or "unikini"), was designed by Rudi Gernreich in 1964, consisting of only a brief, close-fitting bottom and two thin straps; it was the first women's topless swimsuit. Gernreich's revolutionary and controversial design included a bottom that "extended from the midriff to the upper thigh" and was "held up by shoestring laces that make a halter around the neck." Some credit Gernreich's design with initiating, or describe it as a symbol of, the sexual revolution. The image to the left is of a woman wearing a monokini in 2010. One-piece(also known as tank suit, maillot, or singlet) Probably the most common form of swimsuit, this is the inspiration for the tank top as a mainstream article of clothing. The name "tank suit" is also supposed to be derived from the term "swimming tank", an obsolete term for what is now called a swimming pool. Also called a singlet from which evolved the wrestling singlet. A male under-garment in the same form was also called a singlet. Tankini(also known as two piece) One piece covers the breasts and stomach (like a tank top), the other the crotch and buttocks. Invented in 1998 by Anne Cole (1926–2017), the founder of the brand Anne Cole. Tank top and pants Tank top covering pants prevents water parachuting pants off.

Men's swimsuits Name Image Description Boardshorts (also "boardies" in Australia) Boardshorts are a longer version of trunks that come to or past the knee. They usually have a non-elastic waistband, and will give a tight fit around the torso. Boardshorts were originally developed for various board sports such as surfing, paddleboarding, and wakeboarding. Jammer A type of men's swimwear worn primarily by competitive athletes, somewhat resembling cycling shorts or compression shorts. Square cut swim trunks A swimwear style similar to swim briefs, but with a more conservative cut. They can be compared to boxer briefs but with nylon/spandex composite or polyester fabric. Swim briefs(also known as racing briefs, Speedos, competition briefs, bathers, brief or low rise sungas, racer bathers, trunks, or "swimmers" in Australia) Swim briefs, often made of wool and held in place with a military-style canvas belt at the waist, go back at least to the 1930s. They can be seen in hundreds of print ads, worn by muscleman Charles Atlas, and were very popular. Although in a style that today appears similar to underwear briefs, it is likely that the swimwear preceded the underwear, A nylon version (without the belt), pictured at left, was launched at the 1956 Melbourne Olympics by Speedo. Swim briefs are now often made of a nylon and spandex composite, while some longer lasting suits are made from polyester. The style varies from a full seat to thong or g-string. Most swim briefs have a beige or white lining on the inside front made of a similar fabric. Tank top and pants Tank top covering pants prevents water parachuting pants off. Trunks(also known as swim trunks generally, also known as boardshorts in Australia or shorts in UK) In the US, this describes a loose, mid-thigh style of swimwear, made of 100% polyester or 100% nylon fabric. They are usually shorter than boardshorts but longer than boxer shorts. They feature a polyester liner inside the shorts. Although trunks have been used as swimwear since the 1940s, their heyday was in the 1990s when they were highly popularized thanks in part to TV shows like Baywatch. Today, they have been eclipsed by boardshorts for beachwear among teenagers and young adults in North America and some other places. They remain the norm with older age groups and young children.

In other cultures (particularly the UK), the term "trunks" is used to describe swim briefs, although it has been increasingly common for any men's swimwear to be generically described as "trunks".

Body coverage