As far as I am concerned price is roughly the same for natural and synthetic rubber production, but synthetic rubber is used more often. Though, thanks for fillers idea. Definately will look something about them.
Good day, have been doing research on sustainable synthetic materials used for rubber and besides goodyear's Bio isoprene and yokohama's orange oil use have not found anything more or less interesting. I just blame my searching skills for this, I can not believe that there are close to none...