I can only tell you what it is in terms of materials!

The English name of Santoprene is santoprene, which is a trademark registered by the American Exxon Mobil Company, which is also its manufacturer!

The products of the santoprene series are mainly made by mixing PP (polypropylene) and EPDM (ethylene propylene diene monomer).

The properties are between rubber and plastic, but more towards rubber! This is a relatively commonly used material. As far as I know, it is mainly used in auto parts!