Described are imbibition compositions that incorporate kinetic enhancing additive(s) into photochromic polymeric host material. Kinetic enhancing additives include organic polyol(s), epoxy-containing compound(s) or a mixture thereof that improves the performance of organic photochromic compounds in the polymeric host as determined in the Photochromic Performance Test. Also described is a process for incorporating kinetic enhancing additives into polymeric substrates prior to, after and/or with organic photochromic compounds and the resulting photochromic articles produced by such a process.