Abstract: The invention pertains to a fiber comprising 0.5-30 wt. % based on the weight of the fiber of a composition comprising: a) a Bunte salt (A); b) a polysulfide compound (B) comprising the moiety {S]n— wherein n=2-6; and c) sulfur or a sulfur donor (C). Preferably the polysulfide compound has the formula: wherein n=2-6; R is independently selected from hydrogen, halogen, nitro, hydroxyl, C1-C12 alkyl or alkoxyl or aralkyl; The invention further relates to a vulcanization process for making a fiber-elastomer composition comprising the step of vulcanizing: (a) 100 parts by weight of at least one natural or synthetic rubber; (b) 0.1 to 25 parts by weight of an amount of sulfur and/or a sulfur donor, to provide the equivalent of 0.1 to 25 parts by weight of sulfur; and (c) 0.1 to 20 parts by weight of said fiber.