In conclusion, TG–MS seems to be a useful tool for the interpretation of thermal degradation of polymer blends such as NBR/PVC and the action of the various additives on the blends. It enabled the monitoring of the evolved products at each degradation step, facilitating the comparison of different blends. It appears that the thermal decomposition of NBR/PVC blend consists of two profiles; that of PVC and that of NBR. The mass spectra of the polymer blends with inorganic additives did not reveal any significant changes to the type of decomposition products of the polymers, compared with that of NBR/PVC blend without additives. The most remarkable change is the absence of HCl from decomposition products in the presence of the Mg(OH)2 additive.