Laminated glass has been made since the early 20th century. It was only commonly used after it became compulsory after IIRC the 1930 Road Traffic Act, the problem was that it used cellulose as a laminate that used to absorb moisture and discolour (Yellow 'bubbles' appearing around the screen edges. 'Safety' glass, which was created by heat treating glass was invented later (1930's?), this proved to be cheaper than laminated glass and also easier to create the curves that came into fashion from the late forties. However this would sometimes shatter unexpectedly (The original curved windscreens on the class 309's for example.)