The performance of natural rubber based products, such as engine mounts which are susceptible to degradation caused by heat, oxidation, ozone attack or ultraviolet radiation is significantly improved by coating exposed surfaces of the product with a polymeric material having excellent heat and oxidation resistance properties. By applying such polymeric coatings having high resistance towards oxidation under excessive heat, the C.dbd.C bonds of the natural rubber are protected from oxygen and ozone attacks, thereby allowing its strain-crystallization characteristic properties to be retained.