The ability of a material to resist radiation damage is determined by how well the microstructure can remove vacancies and interstitial defects in equal numbers. However, the exact processes by which this happens are poorly understood, and the search for promising materials has been largely heuristic. On page 1631 of this issue, Bai et al. (1) describe a mechanism in copper that suggests that nanomaterials in general might have exceptional radiation resistance. The authors' interpretation is supported by some previous experimental findings and suggests new directions for trial materials.