A bikini is a women’s two-piece swimsuit featuring two triangles of fabric on top that cover the woman’s breasts, and two triangles of fabric on the bottom: the front covering the pelvis but exposing the navel, and the back covering the buttocks.

In the summer of 1946, Western Europeans enjoyed their first war-free summer in many years. French designers sought to deliver fashions that matched the liberated mood of the people. Fabric was still in short supply, and in an endeavor to resurrect swimwear sales, two French designers – Jacques Heim and Louis Réard  – almost simultaneously launched new two-piece swimsuit designs in 1946. Heim launched a two-piece swimsuit design in Paris that he called the atome, after the smallest known particle of matter. He announced that it was the “world’s smallest bathing suit.” Although briefer than the two-piece swimsuits of the 1930s, the bottom of Heim’s new two-piece beach costume still covered the wearer’s navel.

Soon after, Louis Réard created a competing two-piece swimsuit design, which he called the bikini. He noticed that women at the beach rolled up the edges of their swimsuit bottoms and tops to improve their tan. On 5 July, Réard introduced his design at a swimsuit review held at a popular Paris public pool, Piscine Molitor, four days after the first test of an US nuclear weapon at the Bikini Atoll. The newspapers were full of news about it and Réard hoped for the same with his design. Réard’s bikini undercut Heim’s atome in its brevity. His design consisted of a two triangles of fabric forming a bra, and two triangular pieces of fabric covering the mons pubis and the buttocks connected by string.

When he was unable to find a fashion model willing to showcase his revealing design, Réard hired Micheline Bernardini, an 18-year old nude dancer from the Casino de Paris. He announced that his swimsuit, was “smaller than the world’s smallest bathing suit”. Réard said that “like the [atom] bomb, the bikini is small and devastating”.Fashion writer Diana Vreeland described the bikini as the “atom bomb of fashion”. Bernardini received 50,000 fan letters, many of them from men.Photographs of Bernardini and articles about the event were widely carried by the press. The International Herald Tribune alone ran nine stories on the event. French newspaper Le Figaro wrote, “People were craving the simple pleasures of the sea and the sun. For women, wearing a bikini signaled a kind of second liberation.

Heim’s atome was more in keeping with the sense of propriety of the 1940s, but Réard’s design won the public’s attention. Although Heim’s design was the first worn on the beach and initially sold more swimsuits, it was Réard’s description of the two-piece swimsuit as a bikini that stuck. As competing designs emerged, he declared in advertisements that a swimsuit could not be a genuine bikini “unless it could be pulled through a wedding ring.” Modern bikinis were first made of cotton and jersey.