A woman wearing a fashionable bathing costume, circa 1870.
A woman wearing a fashionable bathing costume, circa 1870.Hulton Archive—Getty Images
A woman wearing a fashionable bathing costume, circa 1870.
Holidaymakers posing in bathing suits in the ocean surf at Santa Monica, California, circa 1890.
Woman in one-piece bathing suit and cap reclining on a beach in France, circa 1900.
A Girl in A Bathing Costume, circa 1909.
Annette Kellermann 1910
Four young women in matching beach wear run out of the surf, Los Angeles, California, circa 1910.
Actress Elsie Marson in a red silk swimsuit with white embroidered spots, circa 1918.
French Woman In A Bathing Suit circa 1920.
Woman having her swimsuit measured for length violations on a Washington DC beach, circa 1922.
Five women walking arm-in-arm on the beach wearing wool bathing suits, circa 1925.
A bathing dress, circa 1926.
Alice Nikitina wearing a striking bathing suits at the beach in Italy, Alassio, Italy, circa 1929.
Belted one-piece jersey bathing suits with stripes on the bottom; designed by Lucien Lelong, circa 1929.
Swimsuit fashion in Paris, France, circa 1930.
Woman wearing funny swimming suit at the Aquatic gala at Molitor swimming pool, on June 23, 1931 in Paris, France.
Verna Lee Fisher sporting her newly created crossword swimsuit with matching bathing hat, at Palm Beach, Florida, circa 1933.
The Latest In swimwear on a beach In California, circa 1934.
Actresses Ida Lupino and Kathleen Burke model the latest swimwear circa 1935
Actress Alexis Smith in a swimming costume running along the beach in southern California, USA circa 1940.
Bathing suit clad female members of the British Imperial Censorship Staff, who call themseleves the censorettes, standing poolside at the Princess Hotel, which also serves as their offices on the island. Circa 1941.
Model posing in bathing suit in Florida, circa 1945.
Two models wearing bathing suits and bathing caps, circa 1946.
The first bikini designed by Louis Reard, 1946.
A woman wearing a fashionable bathing costume, circa 1870.
Hulton Archive—Getty Images
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See How Swimsuits Evolved From Victorian Times to the Bikini Age

Think it's hot at the beach these days? Imagine wearing wool, which is what the first garments we'd recognize as swimsuits were made of.

But maybe wool had its charms.

"Our forebears knew that wool offers protection against chills," LIFE noted in a July 1, 1940, spread on the latest trends in swimsuits: that season's brave yet "vain" women "gladly shivered for fashion's sake" in cotton and rayon.

That's just one of the surprising tidbits gleaned from wading through the above photos, which trace the evolution of swimsuits from Victorian-era bathing costumes to the bikini. Advances in mass transit and the spread of the idea of leisure time made the beach more accessible to more people starting in the mid-19th century, so it makes sense that that would be when bathing suits designed for leisurely swims became available. In the 1870s, swimsuits in North America involved corsets, bathing shoes and hose, according to World Clothing and Fashion: An Encyclopedia of History, Culture, and Social Influence.

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The sleeveless one-piece became especially popular in 1907 after police arrested Australian professional swimmer Annette Kellermann for indecency when she wore one at Revere Beach north of Boston. "By promoting swimming as exercise for women and for Olympic competition and vaudeville, Kellerman continued to influence skirtless, sleeveless beach and performance wear," World Clothing and Fashion notes.

More form-fitting styles came out in around the 1930s with the development of new and stretchier synthetic fabrics.

Two-piece swimsuits did exist by then, but they mostly covered up the belly button until July 5, 1946, when 19-year-old French model and dancer Micheline Bernardini debuted the four fabric triangles known as a "bikini" at the popular swimming pool Piscine Molitor.

Created by Louis Reard, it made a bigger splash than a similar suit, the Atome, that had been released earlier that year by Jacques Heim. The simple reason: it used even less fabric. Both names spoke to a particular moment in history: their names referenced the development of atomic weapons. (Bikini Atoll was famously the site of atomic-weapons testing.) People at the time lived with the fearsome knowledge that nuclear war was now possible, but also with the hope that the science behind the bomb might lead to great advances. As TIME explained the significance of the timing of Reard's invention when the bathing suit celebrated its 50th anniversary:

Two years earlier, the French had enjoyed the euphoria of liberation from the Nazi Occupation. The tiny suit was named the bikini , in honor of the tiny Pacific atoll where the U.S. was testing atom bombs.... Designer Louis Reard , a onetime engineer with Renault, the car company, had been turning out modest knit bathing suits since 1925, but in 1946 he realized that with the return of peace, people would want to start enjoying themselves again.

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