A partially hydrogenated butadiene acrylonitrile copolymer designed primarily for applications requiring excellent resistance to heat, ozone and non polar hydrocarbon fluids. Special low RDB - type to increase crosslink density for high module and low compression set applications. While sulfur curing systems can be used for improved dynamic properties and adhesion to steel and textile reinforcing materials, peroxide/coagent systems are recommended. High molecular weight provides for capacity of high plasticizer and filler loads.