Abstract: A vulcanizable rubber composition comprising: (A) a diene-containing rubber; (B) a nitrile rubber modified-thermoplastic copolymer of an olefinically unsaturated nitrile and an ester of an olefinically unsaturated carboxylic acid; and (C) a vulcanizing system, wherein the amount of (B) is in the range from 3 to 100, preferably from 5 to 75, and more preferably from 15 to 50, parts solid weight per 100 parts solid weight of (A). The composition retains the desirable low temperature performance of the diene-containing rubber, but has better processability (as measured by mill release, die swell, green strength, etc.) than the diene-containining rubber, as well as improved resistance to attack by organic chemicals, and improved permeation resistance to organic fumes and fluids.