Delrin, Polyamide, Polyacette, Hostaform, Polystyrol, Lucite, Acrylic, Perspex and Bakelite were all part of a new medium of 1960's & 70's plastic watchmaking (the first all plastic watch-->link). With flexible materials came flexible designs and like animated characters in a cartoon, the creators were able to push limits of the physical world.
Some vintage polymer highlights...
And just to point out, these are all mechanical (manual wind-up and automatic) watches. The Swatch revolution was still 10-15 years away.
Vintage Plastic Explosives - Early Polymer Watchmaking
Source: watchismo.blogspot.com