This paper discusses the penetration behavior of fully supported sandwich panels with micro-lattice and foam cores, and composite skins. This behaviour is of importance during foreign object impact and perforation of sandwich structures. Experimental results are given for quasi-static penetration of micro-lattice and foam blocks, and it is shown that these two cellular materials are comparable. Experimental results are also given for drop weight penetration of fully supported skinned panels, and it is shown that skin failure and core penetration are also similar for the two core materials. It is concluded that there is scope for improving the performance of micro-lattice structure and so making such material superior to that of aluminium foam.