This study dealt with the development of polymeric phase change materials (PCM) with two storage temperatures and their characterization as to application-relevant thermo-physical properties. Thus, on the one hand polypropylene (PP) and high density polyethylene (HDPE, two grades) were blended with paraffin wax (70:30 and 50:50 wt.%), respectively. On the other hand one HDPE grade was blended with either polyethylene glycol (PEG), linear low density polyethylene (LLDPE) and polyamide 6 (PA6; 50-50 wt.%). The blending types included compounding (dispersion via twin screw extruder), statistic mixture (manual blending of granules) and layer mixture (layers of granules). The materials (100 g to 200 g) were exposed statically in air in the melted state (exposure temperature min. 20 °C above the melting temperature of the higher melting component) for up to 1440 h in glass jars. After different exposure times the specimen were characterized as to mixing behavior, thermo-oxidative stability and storage capacity. The main focus was on evaluating their applicability as PCM. The investigated PP-paraffin blends exhibited an insufficient thermo-oxidative stability. In general PP is not applicable as PCM. However, HDPE-paraffin and HDPE-polymer blends are applicable as PCM. The storage capacity of these materials remained constant over the investigated exposure times. During the exposure a thermo-oxidative degraded surface layer was formed, which sealed the specimen and protected it from – if already occurred, further - degradation inside the bulk . For the HDPE-paraffin blends (storage capacity of 100-102 J/g for 50:50 w.%, 61 J/g for 70:30 w.% at 86 °C and 110 J/g for 50:50 w.%, 153 J/g for 70:30 w.% at 136 °C – however the melting peaks overlap partly), which generally did not show any phase separation, the blending type affected the protective surface layer’s formation time: for the compound the surface layer already occurred within an exposure time of 160 h; for the statistic mixtures, the protective surface layer occured after an exposure time of 300 h. This effect correlated with the zero shear viscosity of the materials. The HDPE-LLDPE blends showed partially phase segregation during the exposure to static thermal load. This polymeric PCM exhibited a large storage temperature range with two melting peaks, whereas the dominating peak depends on the local material composition. The storage capacity ranged between136-154 J/g at 128 °C and between 155-184 J/g at 133 °C. For the HDPE-PEG blends (storage capacities of 78 J/g at 66 °C and 110 J/g at 135 °C) and HDPE-PA6 blends (storage capacities of 107 J/g at 135 °C and 33 J/g at 220 °C) the exposure to static thermal load yielded a distinct phase separation, wheras the polymer with the lower density formed the upper layer. The high exposure temperature applied for the HDPE-PA6 blends caused an initial reduction of the storage capacities of both materials in the bulk (9% for HDPE; 6% for PA6 after an exposure time of 240 h). However, the storage capacities did not alter further with increasing exposure time.