Well you can use many materials to make a mold...
Silicone,latex,polyurethane,plaster,clay.....all have their own good properties and are used for different reasons.
I know some people who own fiberglass companies and they use silicone if they want to bring out fine detail....I tried silicone but it was too flimpsy..I had to make a fiberglass jacket to place at the back of the silicone mold. The sillicone had to be added layer by layer when it was tacky and this took alot of time. Latex is too soft and would tear when you remove the fiberglass part from the latex mold.
So i decided to try marble....took the plug to a friend's marble company and they just poured the liquid marble on the plug...Within a couple of hours it was hard...bufffed it,waxed it and applied a layer of mold release
and wa..la.....it was done....The marble mold took me 2 days to make...i wasted alot of time with my silicone mold....but lesson learnt...silicone is expensive though but lucky for me i got it all free...i also recieved 5 gallons of part A and 5 gallons of part B to make Foam...all free....a gallon of each part would cost over $100....Tried it...didnt like it....
Its all good for your own learning and self knowledge...After this i shall be making all my Supra body panels out of carbon fiber or fiberglass or honeycomb....that way I shall obtain more experience and hopefully sell some.
Cheers,
Roy