The term Sweater girl was made popular in the 1940s and 1950s to describe Hollywood actresses like Lana Turner, Jayne Mansfield, and Jane Russell, who adopted the popular fashion of wearing tight sweaters over a cone- or bullet-shaped bra that emphasized the woman's bustline. The term was virtually synonymous with "pin-up girl," a popular culture trope of the Second World War referring to the pretty girls whose pictures adorned soldiers' barracks.
The sweater girl trend was not confined to Hollywood and was viewed with alarm by some. In 1949 a Pittsburgh police superintendent even singled out the sweater girl as a symptom of the moral decline of postwar youth:
"Women walk the streets, their curves accentuated by their dresses," Superintendent of Police Harvey J. Scott said. "But our real problem is with bobby soxers. They are the sweater girls—just kids showing off their curves and apparently liking it. What kind of mothers and wives are they going to be?" 
New, soft fabrics like cashmere and angora were being used to make sweaters. The conical shape bra, sometimes called a bullet bra, raises and separates her breasts. In its original form, the look was often tied to the promotion of new bra technology.
Interest in the bullet bra increased after Madonna wore a cone bra during her 1990 Blond Ambition World Tour. The bra was designed by Jean Paul Gaultier who was inspired by the vintage Perma-Lift bullet bra of the 1940s. By that time, the style was regarded as erotic and provocative. The bullet bra has also become popular with burlesque and rockabilly enthusiasts, both of which draw inspiration from the 1950s.
Lana Turner's appearance in the 1937 film They Won't Forget in a tight-fitting knit top is sometimes considered the first case of the "sweater girl", as Hollywood publicists sought for a catchy phrase to describe the impact she made on the screen. Movie magazines nicknamed her "The Sweater Girl," just as Ann Sheridan was "The Oomph Girl," Dorothy Lamour "The Sarong Girl," and Clara Bow "The It Girl."
From the 1944 Army/Navy Screen Magazine #20, a one-reel short that showed portions of a special Armed Forces Radio Network recording session, Bob Hope introduces "sweater girl" Judy Garland. Before she sings Over the Rainbow, they do a short comedic bit, Judy asking why men are so crazy about sweater girls. Bob says he doesn't know; "That's one mystery I'd like to unravel". 
In September 1968 an obscure clerical worker named Francine Gottfried briefly attained international celebrity as "Wall Street's Sweater Girl" as large crowds of gawking men and newspaper reporters awaited her arrival at the Wall Street subway stop each morning and mobbed her on her way to work.
- Herbst, Philip (2001). Wimmin, wimps & wallflowers: an encyclopaedic dictionary of gender and sexual orientation bias in the United States. Intercultural Press. p. 122. ISBN 978-1-877864-80-3.
- Ostler, Rosemarie (2005). Dewdroppers, waldos, and slackers: a decade-by-decade guide to the vanishing vocabulary of the twentieth century. Oxford University Press US. p. 85. ISBN 978-0-19-518254-5.
- "Plunging neckline, falsies get blame for rise in sex crime," Brooklyn Eagle, December 16, 1949. Retrieved July 9, 2014.
- Madonna on the Blond Ambition World Tour
- The Internet Movie Database
- National Archives 1943