Lower tension set properties were also observed, indicating the better elastomeric nature of the material. Moreover, the TPV without compatibilizer showed larger vulcanized rubber domains and bigger cavitations. Among the three types of blend compatibilizers, PhHRJ-PE gave TPVs with the best overall properties because the block copolymer compatibilizers promoted the highest compatibility with stronger linkages in the molecules and forming the smallest vulcanized rubber domains in the HDPE matrix. Therefore, PhHRJ-PE was chosen to be a compatibilizer for MNR/HDPE TPVs.