(1) for moulding a container starting with a parison (3) in plastic material, comprising: two half-moulds (4a, 4b) defining at least one housing cavity (5) for the parson (3); a stretching rod (23), made of metal material and insertable into said parson (3) to stretch it; a hollow body (25), made of metal material, sized so as to envelop at least partially the parison (3) placed in said housing cavity (5), a voltage difference being applied between the stretching rod (23) and the hollow body (25) so as to generate a plasma inside said housing cavity (5), said plasma having a pressure equal to or higher than the atmospheric pressure.