Abstract The dynamic mechanical properties of natural rubber and bromobutyl rubber (used in automotive suspension parts) were investigated to determine the effect of particle size of carbon black filler and state of cure of the rubber matrix. The results indicate that state of cure has little effect on storage modulus (hardness and stiffness). However, elastomers with a desirable storage modulus, with low sensitivity to temperature change, can be developed using a filler with a small particle size.