Alex,
They were talking about resin casting, or more accurately, using room temperature vulcanising latex rubber to make a mold of something, then using polyurethane resin to cast copies in the mold.
Often, there is too much fine detail, or undercuts in the mold to allow a clean cast, so some folks place the resin filled mold in a vacuum chamber and evacuate the air from it to remove all of the air from the resin - this prevents "skips" in the detail of the par or bubbles in the resin.
There are several pretty goot articles in FSM about resin casting. If you want to have a look at them, I can tell you which mags have the articles. Just email me using the link below and ask.
Otherwise, I have been producing masters and resin castings in production run batches for years and selling them to a local retail outlets, and have lots of experience. If you have any questions, I'm all too happy to answer them.
Cheers,
LeeTree