Metals across all industries demand anti-corrosion surface treatments and drive a continual need for high-performing and low-cost coatings. Ordered thin films comprising aligned inorganic platelets dispersed in a polyelectrolyte polymer matrix provide a new class of transparent conformal barrier coatings for protection in corrosive atmospheres. For example, films assembled via layer-by-layer deposition, as thin as 90 nm, are shown to reduce copper corrosion rates by >1000 in an aggressive H2S atmosphere. These coatings can provide high-performing anti-corrosion treatment alternatives to costlier, more toxic, and less scalable thin films, such as graphene, hexavalent chromium, or atomic layer deposited metal oxides.