Method for the production of a hollow body made of plastic having a fluorinated inner surface, showing a locally selective barrier effect, by the fact that in one or more defined regions of the inner surface, the fluorine occupancy deviates from the mean fluorine occupancy by at least ± 10%, preferably by at least ± 30%, and more preferably by at least ± 50%, comprising the following method steps: - extrusion of a parison from a thermoplastic, - blowing of the parison to give a hollow body within a closed cooled supporting mould with a fluid so that the hollow body fills the inner contours of the supporting mould, and - filling of the hollow body with a fluorine-containing gas during the cooling process, wherein: (i) - the gap width of the extrusion die is varied so that one or more defined zones of the parison have predetermined different wall thicknesses; - whereby during said blowing of the parison the wall thicknesses are increased/reduced in one or more defined regions of the hollow body and so this way the cooling of the inner surface in said defined regions being this way effected more slowly/faster, and fluorine being incorporated in the defined regions of the inner surface to a greater/lesser extent owing to the higher/lower temperatures of the defined regions; or (j) - the cooling is reduced in one or more defined zones of the supporting mould and the cooling of those regions of the inner surface of the hollow body which are congruent with these zones taking place more slowly, fluorine being therefore incorporated to a greater extent in the congruent regions of the inner surface owing to the higher temperatures of the congruent regions. - extrusion of a parison from a thermoplastic, - blowing of the parison to give a hollow body within a closed cooled supporting mould with a fluid so that the hollow body fills the inner contours of the supporting mould, and - filling of the hollow body with a fluorine-containing gas during the cooling process, wherein: (i) - the gap width of the extrusion die is varied so that one or more defined zones of the parison have predetermined different wall thicknesses; - whereby during said blowing of the parison the wall thicknesses are increased/reduced in one or more defined regions of the hollow body and so this way the cooling of the inner surface in said defined regions being this way effected more slowly/faster, and fluorine being incorporated in the defined regions of the inner surface to a greater/lesser extent owing to the higher/lower temperatures of the defined regions; or (j) - the cooling is reduced in one or more defined zones of the supporting mould and the cooling of those regions of the inner surface of the hollow body which are congruent with these zones taking place more slowly, fluorine being therefore incorporated to a greater extent in the congruent regions of the inner surface owing to the higher temperatures of the congruent regions. (i) - the gap width of the extrusion die is varied so that one or more defined zones of the parison have predetermined different wall thicknesses; - whereby during said blowing of the parison the wall thicknesses are increased/reduced in one or more defined regions of the hollow body and so this way the cooling of the inner surface in said defined regions being this way effected more slowly/faster, and fluorine being incorporated in the defined regions of the inner surface to a greater/lesser extent owing to the higher/lower temperatures of the defined regions; or - the gap width of the extrusion die is varied so that one or more defined zones of the parison have predetermined different wall thicknesses; - whereby during said blowing of the parison the wall thicknesses are increased/reduced in one or more defined regions of the hollow body and so this way the cooling of the inner surface in said defined regions being this way effected more slowly/faster, and fluorine being incorporated in the defined regions of the inner surface to a greater/lesser extent owing to the higher/lower temperatures of the defined regions; or (j) - the cooling is reduced in one or more defined zones of the supporting mould and the cooling of those regions of the inner surface of the hollow body which are congruent with these zones taking place more slowly, fluorine being therefore incorporated to a greater extent in the congruent regions of the inner surface owing to the higher temperatures of the congruent regions. - the cooling is reduced in one or more defined zones of the supporting mould and the cooling of those regions of the inner surface of the hollow body which are congruent with these zones taking place more slowly, fluorine being therefore incorporated to a greater extent in the congruent regions of the inner surface owing to the higher temperatures of the congruent regions.