Research was conducted to obtain design data of latent heat-of-fusion thermal energy storage (LHTES) devices. The devices studied utilize a porous medium (PM) to increase the effective conductivity of the storage system. Therefore the melting and freezing process is accelerated. Metal shavings and metal spheres were used as porous media and water as the phase change medium (PCM). A simple experimental method to measure the conductivity of a water-metal mixture or ice-metal mixture was applied to obtain conductivity data. These measurements can be considered fairly accurate because measured conductivity of pure water and of pure ice agreed very well with those of accepted tables. The comparison of the measured conductivity for porous media with values obtained from several formulas from the literature showed that no formula predicts the conductivity with an acceptable accuracy.