My grand-uncle had some patents on automobile accessories made of formed plexiglass,as far as I remember it needed high temperatures to be formable.I think it then was molded over iron stamps.These were called Aerorex-Windabweiser,a kind of additional wind-screen to put on the front side windows to prevent draft when driving your Mercedes with an open window .
That invention and others made him a millionaire back in the sixties....
