Suitable examples of silicon containing compounds which are known to impart hydrophobic properties to materials such as carbon black and fillers are hexamethyldisilazane, trimethylethoxysilane, trimethylchlorosilane, dimethyldiethoxysilane, vinyldimethylacetoxysilane, trimethylsilylisopropylamine, trimethylsilylethylamine, phenyldimethylsilypropylamine, vinyldimethylsilybutylamine, diethylaminoxyt