What he's calling plastic I'd call a paper based phenolic insulator.
Like seen here
https://www.atlasfibre.com/sheets/The cotton based phenolic last near forever. On my truck I'd like to add some terminals to those strips for turn signals too, which will require machining new strips and reusing the old hardware. You could do the same to duplicate the original if you didn't want to buy the reproductions (most that I've seen aren't great quality).
