A multicomponent polymer blend composition is prepared by intimately mixing a halogenated thermoplastic, a selectively hydrogenated monoalkenyl arene-diene block copolymer, and at least one dissimilar engineering thermoplastic resin under such conditions that at least two of the polymers form at least partial continuous network phases which interlock with the other polymer networks and therefore results in a desirable balance of properties. These blends have an unobviously high heat distortion temperature relative to the improved impact strength.