NOVELTY - The method involves applying a barrier coating (4) of a first polymer to the substrate and then applying a protective coating of a second polymer to the barrier coated substrate.    USE - For reducing the gas permeability of a substrate such as film for shrink-wrapping used to wrap fresh meat or poultry or bottles used in the food industry, a petrol tank or paint can, or preform (all claimed). Can also be used for plastic car batteries, plastic wine bottles and plastic wine bags.    ADVANTAGE - Enables application of barrier coatings on articles having nonuniform or irregular shapes such as bottles. Produces a bottle with a very thin, i.e. 1-2 microns thick coated layer, while still providing good gas barrier properties similar to those of coextrusion bottles.    DETAILED DESCRIPTION - Preferred Features: The method involves applying to the natural or synthetic polymer substrate, a first polymer of polyvinyl alcohol, ethylene-polyvinyl alcohol copolymer or polyvinylidene dichloride and then the second polymer consisting of polyesters and copolymers of polyesters, polycarbonates, polyolefins, polyvinyl chloride, polyamides and aliphatic polyketones. The second polymer may be polyethylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene and polystyrene. The second polymer has a molecular weight between 10000-30000, a viscosity between 0.40-0.80 and a softening point of 120-180 degrees C. The protective coating is formed by applying a solution of the second polymer dissolved in a volatile solvent at temperature close to the solvent's boiling point. The substrate and barrier coated substrate may be preheated by flame treatment or corona discharge prior to application of the barrier coating and protective coating respectively to improve coating adherence. An adhesive such as methoxymethylmethylolmelamine or a polyester based adhesive may alternatively be used to improve adhesion. A third barrier coating the same as the first may be applied before application of the protective layer. The coated substrate has an oxygen transmission rate of less than 10, preferably less than 3, cubic cm/square m/day at ambient temperature and humidity. The coatings are applied by spray, dip or roll coating. When the substrate is a preform the preform is expanded by blow molding, the first polymer becoming oriented during expansion to reduce its gas permeability.    An INDEPENDENT CLAIM is included for a substrate formed using the above method, the substrate being a preform, a plastic bottle or a film suitable for shrink wrapping (all claimed).    DESCRIPTION OF DRAWING(S) - The drawing shows a preform after application of a barrier coating.    barrier coating (4)