A partially hydrogenated butadiene acrylonitrile ter-polymer for applications requiring good flexibility at low temperature featuring particularly low mould fouling properties. Designed primarily for dynamic applications requiring excellent resistance to heat, ozone and good resistance to non polar hydrocarbon fluids. Sulfur curing systems are used for improved dynamic properties and adhesion to steel and textile reinforcing materials. However, peroxide/coagent systems can be used for improved resistance to heat and compression set.