The combination of irradiation tolerance, high strength, and thermal stability is a key requirement for structural materials used in nuclear reactor cores. It is challenging to develop bulk materials possessing all three properties because of apparently intrinsic trade-offs among them. We report a novel interface engineering strategy that simultaneously achieves superior irradiation tolerance, high strength, and high thermal stability in bulk nanolayered Cu-Nb composites. By synthesizing Cu-Nb composites containing interfaces with controlled sink efficiencies, we design a material in which nearly all irradiation-induced defects are annihilated. In contrast to grain boundaries in single-phase metals, the Cu-Nb interfaces in these composites remain stable and void free. Interface engineered bulk composites are adaptable to large-scale industrial production and exemplify an innovative approach to design interface-dominated materials that eliminate the trade-offs that constrain conventional alloy design. References: Acta Mater 60 (2012) 6341, Adv Mater 25 (2013) 6975 and JNM 452 (2014) 57.