EGECat® CopperOct and EGECat® PotassiumOct serves as synergistic with cobalt promoters in unsaturated polyester resin curing. It reduces the “pinking” effect of cobalt while alters the gel time and the exotermic temperature peak at the curing. Although they both exhibit synergetic effect with cobalt accelerators, the former is rather an inhibitor and the latter works as promoter.