A series of segmental polyurethane organic inorganic hybrids with polyhedral oligomeric silsesquioxanes (POSS) incorporated along the chain contour on the hard segments is irradiated by γ radiation at doses up to 100 kGy. The effects of this treatment on the morphology of the materials and the low temperature stability to oxidation are assessed complementary by non-isothermal and isothermal chemiluminescence experiments as well as with differential scanning calorimetry. From the methodological point of view, it was found that both physical and chemical processes have a footprint on both methods, but the physical ones manifest themselves more intensely in the thermal method, whereas chemical ones in chemiluminescence. Due to γ-exposure the onset oxidation temperatures decrease by several degrees, but POSS seems to protect the material to some extent. γ-Irradiation damage has also a negative effect on the development of phase separation, which is further enhanced by the presence of POSS. The crystallinity of the soft segments in the matrix is completely suppressed by irradiation, however, even a small amount of POSS preserves the phenomenon. •Physical events in polyurethanes have a small but observable CL footprint.•γ−irradiation makes material more vulnerable to thermal oxidation.•POSS protects to some extent from the effects of irradiation.