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.