The influence of parameters contributing to rubber stiffness, including, crosslink density, hardness, and modulus, on the crack growth and abrasion resistance of carbon black-filled purified natural rubber (PNR) vulcanizates as well as a whole natural rubber (WNR) vulcanizate counterpart or a control were elucidated. In addition, the tensile properties of PNR and WNR were also determined. PNR containing the same curative level as that of the control had lower stiffness and exhibited superior crack growth resistance. The results revealed that the improved crack growth resistance of PNR, compared to the control, was due to its lower crosslink density, hardness, and modulus. In addition, the tensile strength and abrasion resistance of PNR vulcanizates were not as sensitive as the crack growth resistance to the changes of their stiffness. (C) 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1793-1796, 2003.