Abstract The thermal stability of blends of polyurethane with three different elastomers having reactive functional groups has been studied. The blends have been prepared by three different blending techniques, keeping the blending ratio constant. It was found that the thermal stability of the blends was dictated by the blending technique. Blends prepared by the masterbatch technique degraded at a lower temperature. The degradation temperatures were increased when preblending and preheating/preblending techniques were adopted. This may be due to the formation of interchain crosslink bonds between the two elastomer phases, the extent of which was more in the preheated/preblended technique.