Hydrothermal weathering of the peroxide vulcanized specimens of silicone rubber, EPDM rubber, and their 50 : 50 blend carried out for various durations at different temperatures reveals that silicone is very susceptible to degradation. For example, the modulus, the strength, and the elongation at break consistently fall with aging period. For 72 h of aging at 210-degrees-C, it practically loses it rubberiness (elongation < 50%); while EPDM and the 50 : 50 blend maintain more than 100% elongation at break during the times and temperatures. While hydrolytic chain scission is the main degradation mechanism for silicone, EPDM undergoes a predominantly crosslinking reaction. The kinetics study reveals that the better retention of properties of the blends over silicone is due to an increase in the activation energy of degradation in the presence of EPDM rubber, and this protection effect is higher in liquid-phase weathering than in steam-phase weathering.