Treated glass fibers (RICS, 3 and 6 mm in length) were added at a concentrations of 10, 20, and 30 phr in natural rubber (NR), nitrile rubber (NBR), and ethylene-propylene-diene comonomer (EPDM) formulations, in both plain and carbon black mixes. The compounds were mixed in two-roll mill and were evaluated for their resistance to hot-air aging, abrasion, compression set, Goodrich heat buildup, De Mattia fatigue, and for NR mixes, adhesion in the tensile mode. The vulcanizates of the three rubbers showed resistance to hot-air aging. Abrasion resistance was poor for NR, and it improved with carbon black addition in the presence of treated glass fiber in NBR. In carbon-black-added EPDM vulcanizates, the abrasion resistance and fatigue resistance were better. (C) 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1124-1135, 2004.