A piston with a cooling gallery containing an open cell radiator is provided. The radiator has a large thermally conductive surface area that acts as a heat-sink to remove heat from the piston. Heat from the piston is transmitted from the radiator to cooling oil that enters the cooling gallery via an oil inlet formed in a floor of the cooling gallery and exits the cooling gallery via an oil outlet. The piston comprises a piston body including an upper part presenting an upper combustion surface and an undercrown surface. A ring belt depends from the upper combustion surface, and the cooling gallery extends around the piston body beneath the undercrown surface radially inwardly of the ring belt. The radiator includes a plurality of fins extending annularly around the cooling gallery. The fins of the radiator are spaced from one another by gaps extending annularly around the cooling gallery.