NOVELTY - Method for the improvement of the barrier properties of ethylene homo- or copolymer composition against the permeation of hydrocarbons, where the ethylene homo- or copolymer comprises at least one sterically hindered amine compound in an amount of 100 to 10000 ppm, calculated on total weight of the polymer, involves subjecting at least one surface of a hollow body made of the ethylene homo- or copolymer to fluorination.    USE - For the improvement of the barrier properties of ethylene homo- or copolymer composition against the permeation of hydrocarbons, used in articles of plastic and components for the transport and storage of liquid fuels comprising biodiesel, such as vegetable oil esters, or methanol, preferably plastic fuel tanks for automotive vehicles or heating oil tanks or chemical storage or transport containers (claimed), plastic fuel tanks and parts such as pipes and feed-lines, bottles, canisters and drums; and in automotive industry, where plastic fuel tanks are comprised in automotive cars driven by combustion engines.    ADVANTAGE - The method improves barrier properties of composition. The cold temperature of the fluorinating gas provides an additional cooling effect at the inner surface of the hollow article helping thereby to shorten the whole manufacturing process.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) use of sterically hindered amine compounds to improve hollow bodies made of an ethylene homo- or copolymer composition against permeation of hydrocarbons comprised in it, after treatment of at least one surface of such hollow bodies by fluorination, so that at least one sterically hindered amine compound has the formula (I) or (II); and    (2) articles of plastic and components for the transport and storage of liquid fuels comprising biodiesel, such as vegetable oil esters, or methanol, preferably plastic fuel tanks for automotive vehicles or heating oil tanks or chemical storage or transport containers produced by the method.    n=2 to 20.