CuO nanoparticle-doped hierarchical porous polymeric frameworks can be used for shape stability of octadecanol (OD) as a phase change material (PCM) for latent heat energy storage (LHTES) applications. A hierarchical porous foam polymer was synthesized by high internal phase emulsion polymerization of styrene and divinylbenzene doped with/without CuO. The synthesized high internal phase templated polymers (PHPs) with hierarchical pores were capable of absorbing up to 75 wt % OD without seepage behavior. The morphological, structural, and thermal behavior of PHPs/OD and PHPs@CuO/OD composite PCMs was determined using scanning electron microscopy (SEM)/energy-dispersive X-ray analysis (EDX), Brunauer-Emmett-Teller (BET) surface area analyses, Fourier transform infrared spectrophotometry (FT-IR), differential scanning calorimetry (DSC) analysis, and thermogravimetric analysis. Thermal analysis results revealed that PHP containing 75 wt % OD has an LHTES capacity of 190.4-194.0 J/g in the temperature range of 52.0-53.0 degrees C. The chemical and thermal stabilities of the developed composite PCMs were tested with repetitive thermal cycles. After 0.25 wt % CuO nanoparticle doping, the thermal conductivity of the composite PCM increased up to 86 and 17% compared to PHP and pure OD, respectively. Heat storage/releasing times of PHP@CuO/OD reduced about 20-22% relative to those of PHP/OD because of improved thermal conductivity. The thermal stability of PHP/OD and PHP@CuO/OD composites increased from 196 to 278 degrees C and 251 degrees C, respectively, compared to pure OD. The results exposed that especially PHP@CuO/OD composite PCMs are good candidates for LHTES applications because of their considerably high LHTES capacity.