Technical properties such as hardness, tensile strength, ultimate elongation, and rebound resilience are popular in quality control, but the trend in these properties shows a generalized picture of the structure-property relations. Test specimens were aged in hot air by systematically varying the time and temperature from 24 to 96 h at 70 to 100 degreesC. For an effective comparison the observed values were plotted as a function of time, temperature, and formulations. The data thus obtained were correlated with shelf-aging in particular cases, and it was observed that aging at 100 degreesC for 24 h could be used for such formulations. A "sulfur donor" system cured nitrile-butadiene rubber (NBR) vulcanizate and an ethylene-propylene-diene (EPDM) vulcanizate showed the best retention of properties. Although the SEM micrograph of the NBK. was in agreement with this observation, the EPDM was not.