An aqueous coating composition comprises (a) a hydrophilic binder; (b) an ester of cellulose having at least 8 acyl groups per C.sub.24 cellulose unit wherein at least a majority of the acyl groups are derived from an aliphatic polycarboxylic acid having from 3 to 6 carbon atoms; or a salt of the ester; and (c) a hardening agent in an amount sufficient to render the composition water-insoluble after coating and drying of the composition. This coating composition is useful for forming water-insoluble, conductive and highly-adherent layers in composite bases or elements, and particularly in photographic elements having hydrophobic supports. The conductive layers can be used, for example, as conducive subbing layers or conductive pelloid layers.