Sequential, double elastomer vulcanization method, system, and composition. First and second immiscible elastomers are mixed together with a first additive package. A first curative system is activated to vulcanize the first elastomer in a dispersed phase of the first elastomer to form a partially vulcanized mixture while maintaining melt flowability of the second elastomer in a continuous phase. Then, a second curative system is activated to vulcanize the second elastomer in the continuous phase. Since the partially vulcanized mixture is melt processable, a second additive package can be introduced to the mixture after activating the first curative system. Or, the second curative system can be activatable at a temperature which is higher than an activation temperature of the first curative system. In this manner, blends of dissimilar elastomers can be vulcanized with independent control of plasticizer, filler and curative distribution.