A method for manufacturing a plug for a container neck, wherein: - during a first step, a skirt of the plug is molded, which skirt: - has a globally tubular shape, defining a central axis (X-X) and provided for surrounding the container neck, - extends, along the central axis (X-X), between a first end, intended to be provided with obturating means for obturating the container neck, such as a bottom wall made with the skirt by molding, and a second end opposite to the first end, and - is provided both with attachment means for removable attachment to the container neck, such as at least one screwing/unscrewing thread around the container neck, and with a retention strip for permanent retention around the container neck, this retention strip being able to pass, by folding, from a molding configuration, in which the retention strip extends, from the skirt, in a direction opposite to the first end of the skirt, to an operating configuration, in which the retention strip extends from the skirt, to the first end of the skirt and is adapted to axially abut against an associated bulge of the container neck during the first opening of the plug; and then - during a second step, a peripheral break line adapted to be broken during the first opening of the plug is cut out in the skirt and which line, before the first opening of the plug, connects, along the central axis (X-X), a removable portion (12.1) of the skirt, including said first end of the skirt and provided with said attachment means, and a non-removable portion (12.2) of the skirt, including said second end of the skirt and provided with said retention strip; and then - during a third step, which is applied once the second step is completed, the retention strip is folded towards the first end of the skirt, until the retention strip passes into its operating configuration, characterized in that, while the break line is cut out during the second step, the retention strip is prefolded, by having the retention strip pass from its molding configuration to a prefolded configuration which is intermediate between its molding and operating configurations, and in that, during the third step, the retention strip is folded from its prefolded configuration to its operating configuration. - during a first step, a skirt of the plug is molded, which skirt: - has a globally tubular shape, defining a central axis (X-X) and provided for surrounding the container neck, - extends, along the central axis (X-X), between a first end, intended to be provided with obturating means for obturating the container neck, such as a bottom wall made with the skirt by molding, and a second end opposite to the first end, and - is provided both with attachment means for removable attachment to the container neck, such as at least one screwing/unscrewing thread around the container neck, and with a retention strip for permanent retention around the container neck, this retention strip being able to pass, by folding, from a molding configuration, in which the retention strip extends, from the skirt, in a direction opposite to the first end of the skirt, to an operating configuration, in which the retention strip extends from the skirt, to the first end of the skirt and is adapted to axially abut against an associated bulge of the container neck during the first opening of the plug; and then - has a globally tubular shape, defining a central axis (X-X) and provided for surrounding the container neck, - extends, along the central axis (X-X), between a first end, intended to be provided with obturating means for obturating the container neck, such as a bottom wall made with the skirt by molding, and a second end opposite to the first end, and - is provided both with attachment means for removable attachment to the container neck, such as at least one screwing/unscrewing thread around the container neck, and with a retention strip for permanent retention around the container neck, this retention strip being able to pass, by folding, from a molding configuration, in which the retention strip extends, from the skirt, in a direction opposite to the first end of the skirt, to an operating configuration, in which the retention strip extends from the skirt, to the first end of the skirt and is adapted to axially abut against an associated bulge of the container neck during the first opening of the plug; and then - during a second step, a peripheral break line adapted to be broken during the first opening of the plug is cut out in the skirt and which line, before the first opening of the plug, connects, along the central axis (X-X), a removable portion (12.1) of the skirt, including said first end of the skirt and provided with said attachment means, and a non-removable portion (12.2) of the skirt, including said second end of the skirt and provided with said retention strip; and then - during a third step, which is applied once the second step is completed, the retention strip is folded towards the first end of the skirt, until the retention strip passes into its operating configuration,