The use of a coating composition comprising: (a) from about 5 to about 50 weight percent solids, the solids comprising from about 10 to about 70 weight percent silica and from about 90 to about 30 weight percent of a partially polymerized organic silanol of the general formula RSi(OH)3, wherein R is selected from methyl and up to about 40% of a group selected from the group consisting of vinyl, phenyl, gamma-glycidoxypropyl, and gamma-methacryloxypropyl, and (b) from about 95 to about 50 weight percent solvent, the solvent comprising from about 10 to about 90 weight percent water and from about 90 to about 10 weight percent lower aliphatic alcohol, wherein the coating composition has a pH of from about 3.0 to about 8.0, for the purpose of improving the surface smoothness of a polymeric substrate, particularly a heat-stabilised, heat-set, oriented polyester substrate, and use of said coated substrate in the manufacture of an electronic or optoelectronic device containing a conjugated conductive polymer.