The invention relates to a method of producing an article comprising an interpenetrating polymer network (IPN) and an IPN comprising article e.g. obtainable by this method. The method comprises providing a polymer substrate e.g. shaped to provide the desired article and applying it in a reaction chamber, providing at least one monomer for an interpenetrating polymer, exposing said polymer substrate in said reaction chamber to said at least one monomer in the presence of an impregnation solvent comprising CO2 under conditions wherein said CO2 is in its liquid or supercritical state and polymerizing and optionally cross linking said at least one monomer to form an interpenetrating polymer in the presence of a polymerization solvent under conditions wherein at least a part of said at least one monomer is dissolved in said polymerization solvent. The article comprises a body formed of a polymer substrate and an interpenetrating polymer of a second polymer different from the polymer of the polymer substrate and an outer surface layer on at least a part of its surface of said second polymer.