The Kestos bra was the first commercially produced bra that had two distinct and defined cups and for that we salute them! Early bras were constructed with simple bandeau type tops that supported breasts by compressing them. While they sometimes had seams or a center gathering that distinguished the two sides this definition was very subtle and can't be described as truly separate cups. The vintage flapper bras provide beautiful examples of a compression style bandeau bra that created the compacted bust line desired in the late 1910s and 1920s.
By the 1930s however, new shapes were in style. Rosaline Kiln of the Kestos Corset Company developed what became known as the Kestos bra. After experimenting with handkerchiefs she developed a brassiere that had two completely separate cups drafted with simple darts for depth, and a unique trolley band that buttoned to the bottom of each cup and wrapped around the wearer, crossing in the rear. This new design distributed the weight more efficiently that earlier models and defined the breasts more distinctly. Early advertisements tout its comfort and youthfulness.
Text and image from Partial Coverage.