Adhesive-coated glass fibers (3 and 6 mm in length) were added at loadings 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 a two-roll mill and were characterized for their cure properties, tensile, tear, and Mullin's effect. In NR mixes, all of the formulations showed reversion in cure behavior, suggesting that NR remained unaffected. In NBR and EPDM mixes, almost all of the mechanical properties of the fiber improved. The result was more significant in EPDM than in NBR. (C) 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91:1111-1123, 2004.