Shellac is highly compatible with nitrile rubber and can be incorporated in this rubber on a roll mill up to 50 phr without any difficulty. It acts as an antiscorching agent and plasticizer at processing temperatures. To a small extent, it retards cure increasing the cure time from 30 to 40 minutes at higher concentrations of shellac. This is not harmful in industrial applications. Shellac improves physical properties like modulus, tensile strength, tear resistance, hardness, swelling in hydrocarbon oils to a considerable extent. Resilience remains the same. Abrasion resistance is reduced. Heat generation is more with higher percentage of shellac. It can be seen that the optimum concentration of shellac for the best physical properties is 20 to 30 phr.