What material was the original surround made of?

Have come across several old references to a "very thin rubber surround no longer in production"

But I don't know if that means thin, as in depth of thickness, or thin as meaning the correct roll width and the poster(s) are just referring to foam as "rubber" as in foam rubber

I thought they were all foam on the 117H-1, from beginning to end

please clarify

thank you all