Young Blonde Girl Strips Her White Underwear

In 1913, a New York socialite named Mary Phelps Jacob changed women's fashion forever when she created the first brassiere 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 news of the garment soon spread by word of mouth. By 1914, Jacob had a patent for her design and was marketing it throughout the US. Although women had worn brassiere-like garments in years past, Jacob's was the first to be successfully marketed and widely adopted.
By the end of the decade, trouser-like "bloomers", which were popularized by Amelia Jenks Bloomer (1818–1894) but invented by Elizabeth Smith Miller, gained popularity with the so-called Gibson Girls who enjoyed pursuits such as cycling and tennis. This new female athleticism helped push the corset out of style. The other major factor in the corset's demise was the fact that metal was globally in short supply during the First World War. Steel-laced corsets were dropped in favour of the brassiere.
Meanwhile, World War I soldiers 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. Rayon garments also became widely available in the post-war period.
In the 1920s, manufacturers shifted emphasis from durability to comfort. Union suit advertisements 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.