A coating composition for applying a very thin film coating to a substrate such as a polymeric film comprises a copolymer such as a block copolymer (BCP) that is compatible with the substrate, an alcohol solvent or solvents capable of dissolving the copolymer, a hydrolysed metal alkoxide precursor, a carboxylic acid stabiliser, and an active agent in an ionic, molecular, or small nanoparticle form. The active agent is configured to provide a functionality to the coating composition, selected from antimicrobial, antifungal, barrier, therapeutic, electrical, electronic, magnetic and optical. The composition is a sol comprising a continuous non-sedimentable/stable suspension of very small sized (of nano order) amorphous inorganic polymers in their oligomeric or polymeric state, and comprising the active agent dispersed in a hydrolysed metal alkoxide-BCP matrix. Substrates coated with very thin coatings are also provided, including coated LDPE which is activated before coating by UV/ozone, plasma or corona treatment prior to deposition of a wetting layer.