1900s

By the early 20th century, the mass-produced undergarment industry was booming, and competition forced producers to come up with all sorts of innovative and gimmicky designs to compete. The Hanes company emerged from this boom and quickly established itself as a top manufacturer of union suits. Textile technology continued to improve, and the time to make a single union suit dropped from days to minutes.

Meanwhile, designers of women's undergarments relaxed the corset. The invention of new, flexible but supportive materials allowed them to remove the whalebone and steel while still providing support.

1910s

The increase in the number of underwear manufacturers necessitated the birth of undergarment advertising. The first underwear print advertisement in the United States ran in the Saturday Evening Post in 1911 and featured oil paintings by J.C. Leyendecker of the "Kenosha Klosed Krotch". Early underwear advertisements placed emphasis on durability and comfort; fashion was never a selling point.

By the end of the 1910s, Chalmers Knitting Company split the union suit into upper and lower sections, effectively inventing the modern undershirt and drawers. Women wore lacier versions of this basic duo known as the camisole and drawers.

In 1913, a New York socialite named Mary Phelps Jacob changed women's fashion forever when she cobbled the first brassiere together by tying two handkerchiefs together with ribbon. Jacob's original intention was to cover the whalebone sticking out of her corset, which was visible through her sheer dress. Jacob began making brassieres for her family and friends, and word of mouth soon spread about the garment. By 1914, Jacob had a patent for her design and was marketing it throughout the United States. Although women had worn brassiere-like garments years past, Jacob's was the first to be successfully marketed and widely adopted.

By the end of the decade, Amelia Jenks Bloomer had invented the loosely fitting trouser-like bloomers that bear her name. Bloomers gained popularity with the so-called Gibson girls who enjoyed more athletic pursuits such as bicycling and tennis. This new female athleticism helped push the corset out of style, as well. The other major factor in the corset's demise was the fact that metal was in short supply in much of the world during World War I. Steel-laced corsets were dropped in favor of the brassiere.

Meanwhile, the soldiers of World War I were issued button-front shorts as underwear. The buttons attached to a separate piece of cloth, or yoke, sewn to the front of the garment, and tightness of fit was adjusted by means of ties on the sides. This design proved so popular that it began to supplant the union suit in popularity by the end of the war. Garments of rayon also became widely available in the post-war period.

1920s

In the 1920s, manufacturers shifted emphasis from durability to comfort. Union suit ads raved about "patented" new designs that reduced the number of buttons and increased accessibility. Most of these experimental designs had to do with new ways to hold closed the crotch flap common on most union suits and drawers. A new woven cotton fabric called nainsook gained popularity in the 1920s for its durability. Retailers also began selling preshrunk undergarments.

Women's bloomers became much shorter and stockings covered the legs instead. The shorter bloomers became looser and less supportive as the boyish flapper look came into fashion. By the end of the decade, they came to be known as step-ins, very much like modern panties but with wider legs, worn for the increased flexibility they afforded.

As dancing became a favorite pastime of young flappers, the garter belt was invented to keep stockings from falling. Nevertheless, the increased sexuality of the flapper also made underwear sexier than ever before. It was the flappers who ushered in the era of lingerie.

A Russian immigrant named Ida Rosenthal further developed the brassiere in this decade when she introduced modern cup sizes in 1928 for her company, Maidenform.

1930s

Modern men's underwear was largely an invention of the 1930s. On January 19, 1935 Coopers Inc. sold the world's first briefs in Chicago, Illinois. The company placed a Y-shaped front and overlapping fly on knitted drawers in both short and long styles. They dubbed the design the "Jockey" since it offered a degree of support that had previously only been available from the jockstrap (the company itself would later adopt the name Jockey, as well). Jockey briefs proved so popular that over 30,000 pairs were sold within three months of their introduction.

Meanwhile, other companies began selling buttonless drawers fitted with an elastic waistband, the first true boxer shorts (named for their resemblance to the shorts worn by professional fighters). Scovil Manufacturing also introduced the snap fastener at this time, which became a popular addition to various kinds of undergarments.

Women of this decade brought the corset back, now called the girdle. The garment lacked the whalebone and metal supports and usually came with a brassiere (now usually called a bra) and often garters attached.

1940s

During World War II, elastic waistbands and metal snaps gave way once again to button fasteners due to rubber and metal shortages. Undergarments were harder to find, as well, since soldiers abroad had priority to get them.

At war's end, Jockey and Hanes remained the industry leader, but Cluett, Peabody and Company would make a name for itself when it introduced a preshrinking process called Sanforization, which came to be licensed by most major manufacturers.

Meanwhile, some women readopted the corset once again, now called the waspie for the wasp-shaped waistline it gave the wearer. Many women began wearing the strapless bra, as well, which gained popularity for its ability to push the breasts up and enhance cleavage.

1950s and 1960s

In the 1950s, underwear manufacturers began marketing printed and colored garments. What had once been a simple, white piece of clothing not to be shown in public suddenly became a fashion statement. The manufacturers also experimented with rayon and newer fabrics like dacron and nylon. By 1960, men's underwear was regularly printed in loud patterns or with images ranging from messages to cartoon characters.

Women's undergarments began to emphasize the breasts instead of the waist in the 1950s. The decade saw the introduction of the bullet bra, which featured pointed cups. Fredericks of Hollywood's push-up bra finally hit it big in this decade as well.

Panty hose, which combined panties and hose into one garment, made their first appearance in 1959, invented by Glen Raven Mills of North Carolina. The company later introduced seamless panty hose in the 1965, spurred by the popularity of the miniskirt.

Present day

Underwear as fashion matured in the 1970s and 1980s, and underwear advertisers forgot about comfort and durability, at least in advertising. Sex became the main selling point, bringing to fruition a trend that had been building since at least the flapper era (underwear is the last barrier before nudity, and thus it acts as a sort of gatekeeper to sex). Performers in the 1980s such as Madonna and Cyndi Lauper also got into the act, often wearing undergarments on top of other clothes. Later, in the 1990s, hip hop stars would popularize a similar style, known as the sag, which allowed loosely fitting blue jeans or shorts to droop low, exposing the underwear.

Although it was worn for decades by exotic dancers, the thong first gained popularity in South America, particularly in Brazil, in the 1980s. It was originally a style of swimsuit made so that the back of the suit is so thin that it disappears into the buttocks. By the 1990s, the design had made its way to most of the Western World, and thong underwear became popular. Today, thong underwear is one of the fastest selling styles available among women and is even gaining some popularity among men.

In the 1990s, retailers started selling boxer briefs, which take the longer shape of boxers but maintain the tightness of briefs. Though marketed as a new design, these are actually quite similar to the bottom half of the two-part union suits worn in the 1910s.

Varieties

Today, there are many options in underwear available to men. These include:

• boxer style (at or near true waist, leg sections extending to thighs)
  • woven boxers (traditional)
  • knit boxers (like traditional but with more fabric give)
  • boxer briefs (also knit; more form-fitting)
  • pouch boxer briefs (boxer briefs but with pouch for genitals rather than access flap)
  • athletic-style (skin-tight, usually with no access pouch or flap; like short tights; a variety also is bike shorts)
• jockey shorts (knit fabric, with access pouch or flap; usually at or near true waist, leg bands at tops of thighs)
  • traditional jockey shorts (vertical flap)
  • diagonal flap jockey shorts
  • pouch jockey shorts
  • low-cut jockey shorts
• bikini briefs (usually lower than true waist, often at hips, usually no access pouch or flap, legs bands at tops of thighs)
  • high-side bikini briefs
  • low-side bikini briefs
  • string bikini briefs (the front and rear sections meet in the crotch but not at the waistband, with no fabric on the side of the legs)
• g-string types (with a front pouch for the genitals but no rear coverage)
  • thongs (with a strap securing the pouch at the bottom rear, passing up the crack between the buttocks to the waistband)
  • athletic supporters, also known as jockstraps (with two straps securing the pouch at the bottom rear, passing around the bases of the buttocks up to the waistband at the sides)
  • strapless pouches (with a front pouch and waistband only, no securing straps)

There are also many types of long underwear, union suits, and other variations of men's underwear.

Today, there are many other specialized types of underwear made for sexual purposes. Most of these are meant simply to display the body or genitals in certain ways, while some are intended to provide genital stimulation as well. Frederick's of Hollywood is an example of a business centered around manufacturing and selling such underwear.

Sexualization of undergarments

The modern sexualization of underwear has started one more curious trend: not wearing underwear at all. This practice is known in American slang as freeballing (or freebuffing for females); going commando is also used for both sexes (http://www.wordspy.com/words/gocommando.asp). This trend only emphasizes how far underwear has come from its beginnings as a hygienic aid. When modern people bathe every day, underwear is not nearly as necessary, and with underwear as the final barrier to sex, not wearing it at all is a powerful turn-on for many people.