An experimental investigation of nanoparticle suspensions utilized as nano-enhanced phase change materials (NePCM) was conducted. Cyclohexane-based NePCM samples were prepared with copper oxide nanoparticles with various mass concentrations. Thermal conductivity of the samples was measured using the transient plane source technique for both liquid and solid phases at multiple temperatures. Unidirectional freezing of the samples was investigated and the experimental results were compared with the numerical predictions of a one-dimensional Stefan model proposed earlier by the authors. It was shown that the measured thermal conductivity for samples in their liquid phase is enhanced with increasing concentration of nanoparticles, whereas the data in the solid phase exhibit a non-monotonic enhancement when the concentration is greater than 2%. Unidirectional freezing was found to be expedited by up to 5.2%. ► Cyclohexane enhanced by copper oxide nanoparticles as novel phase change materials. ► Enhanced thermal conductivity measured in both liquid and solid phases. ► Non-monotonic enhancement of thermal conductivity observed in the solid phase. ► Unidirectional freezing observed to be expedited by up to 5.2%. ► Non-monotonic expediting of freezing observed and verified by the Stefan model.