[grosswait]

Definitely not what comes to mind when I think of plastics. I usually hear Bakelite quoted as the first invented plastic.

[pmahoney]

Think "polymer" or "synthetic polymer" since these will be the things bacteria and other parts of nature have not evolved around.

https://en.wikipedia.org/wiki/Polymer#Common_examples

[kube-system]

Synthetic rubber was, in fact, invented after Bakelite.