Hydrogenated Nitrile Rubber (HNBR) is a special elastomer with an unusual property combination; it is grown into a standard material, particularly for synchronous belts for the cramshaft control in the automotive industry besides CR. This report shows the compromising ability of HNBR for dynamic/mechanical properties, its resistance against thermo-oxidative aging, cost effectiveness and aspects of safety, maintenance and ecology. Typical vulcanizates (S- and peroxide cure) for belts are presented and compared in their processing. elongation, crack and heat resistance; where applicable, CR is included.