Nanoarchitected materials have been shown to possess ultra-high mechanical energy absorption due to their unique structure. The exact underlying mechanisms for this high energy absorption are neither well understood nor experimentally identified under realistic conditions. With this proposal we aim to characterize and identify the underlying deformation mechanisms responsible for energy absorption in nanoarchitected composites. We will exploit the unique in situ capabilities of the ID-19 beamline equipped with a Split Hopkinson Pressure Bar. The ultra-high-speed X-ray phase-contrast radiography with large field of view will allow us to capture and correlate failure mechanisms with measured mechanical response over representative material scale. This unprecedented macroscopic in situ characterization of nanoarchitected materials will help us answer critical questions regarding the scalability and viability of nanoarchitecture as a tool for engineering high energy absorbing materials.