This paper first presents an experimental investigation into square metallic sandwich panels with either honeycomb core or aluminium foam core under blast loading, followed by an analytical analysis of their structural response. In analytical modeling, the deformation is divided into three phases, corresponding to the front face deformation, core crushing and overall structural bending and stretching, respectively. The response in the last phase is considered using either small deflection or large deflection theory, based on the extent of panel deformation. The analysis is based on an energy balance and assumed displacement fields. Using the proposed analytical model, an optimal design has been conducted for square sandwich panels for a given mass, and loaded by various levels of impulse. Effect of several key design parameters, i.e. ratio of side lengths, relative density of core, and core thickness is discussed.