it was because of how they designed the bras in those days..
Sweater Girl Glamour 1950s
Picture of typical longline stitched cone bra of the early 50s.Fashion history has shown that by the 1950s glamour was what women wanted most. They had been deprived in the war and they had seen the Hollywood stars that had uplift that almost reached their necks. Brand names like Maidenform, Berlei, Triumph and the British Marks & Spencer bras under the St. Michael label all sold excellent bras that gave the correct pointed circular stitched conical shape of the era.
Right - 1950's Stitched Longline Cone Bra.
The conical bra was the bra that gave the support silhouette for girls who longed to emulate the curves of film star sweater girls like Lana Turner and Jane Russell. Bra history changed for the better as bras began to be revolutionized by the use of nylon, making them lighter, prettier and easier to wash. See 1950's Bra Adverts here.
The 1960s All Change
Picture of Berlei bra.By the 1960s well designed bras by Exquisite Form, Berlei, Twilfit, Lovable, Silhouette, Playtex and the Marks & Spencer St. Michael range were thought ideal under knitted sweater dresses.
Soon Elastomerics transformed foundation garments with power net fabric. Early styling found in bra history became out of tune with modern sixties bra design. The old elastic bra backs and straps were replaced by the newer Courtauld's Spanzelle or Lycra fittings. Overstretched rotted rubber bits that made bras lose their grip were gone forever.