The nitrile polymer to be compounded must be stabilized with an aromatic amine such as di-octyl-diphenylamine. Without this antioxidant, no cadmium/magnesium-cured nitrile compound will give 300'F heat resistance. Ideally, the aromatic amine should be added to the latex after polymerization. However, for polymers which are not stabilized in this manner, the antioxidant may be added during mixing.