The present work is specifically focused on the form stability of paraffin as a phase change material (PCM) through the addition of high-density polyethylene (HDPE). The aim of adding HDPE is to obtain a stable form of paraffin during the phase transition. Moreover, improving the performance of PCM leads to an advanced operation of the latent heat storage unit with an excellent charging duration and response time. The study uses HDPE at a ratio of 5 wt %, 10 wt % and 15 wt %. The results indicate significant differences between the form-stable PCM (FSPCM) and pure paraffin. For instance, the supercooling degree is decreased with the addition of HDPE, where paraffin has a supercooling degree of 8.01 °C while FSPCM with 15 wt % HDPE has a supercooling degree of 3.73 °C. The latent heat of fusion by adding 10 wt % and 15 wt % HDPE is slightly decreased by 1.85 %, which is much lower compared to adding 5 wt % HDPE, which reduces the latent heat of fusion by about 6.02 %. Adding HDPE leads to a faster charging process and a better response time during the discharging process. The charging rate is increased significantly by adding 15 wt % HDPE with a substantial increment of around 40 % with an average charging rate of 2.39 °C/min. The heat release during the discharging process is increased for FSPCM with 5 wt % HDPE where the temperature drops by more than 70 °C within 20 minutes. The findings indicate that adding HDPE contributed positively to reducing the supercooling degree and providing a steady phase transition. Thus, the heat exchange process of paraffin is more favorable, which improves the performance of the latent heat storage unit. Furthermore, the operation can be improved significantly by providing a faster charging and discharging process