Three novel sandwich structure configurations are investigated: i) metallic faces with metallic foam core; ii) metallic faces with aramid paper honeycomb; and iii) aramid fabric faces with aramid paper honeycomb core. Main objective is to define the core's behavior during high-rate compression. In previous tests two collapse modes were identified, but due to the inability of applied testing methods to visualize events in-situ, the sub-surface behaviour is not known, hindering the comprehensive understanding of the collapse mechanism. To address this, we will use synchrotron MHz X-ray phase contrast imaging (MHz-XPCI) measurements coupled to the Split Hopkinson Compression bar (SHPB) to track in-situ damage propagation of the core and compare energy absorption and pressure attenuation properties of specimens.The obtained results will be of great importance for refinement of sandwich typologies and for calibration and improvement of accompanying numerical models used for their design.