Fillers

Reinforcing fillers are added to improve the otherwise poor tensile strength of silicones. Silica in the form of silica fume with a particle size in the 10-40 nm range is the most preferred filler, although carbon black is used. Fillers do interact with the vulcanized rubber to form a pseudo-vulcanization. This can occur during mixing (creep hardening) or during storage (silo aging).

Although grinding can destroy these structures, structure control additives or ant structure additives are often added to counteract these reactions. Examples of these materials are siloxane-based materials such as diphenylsilane and pinacol dimethylsilane.