The present disclosure relates to a manufacturing method for a plug for a container neck. In one implementation, a skirt of the plug is molded and provided with an attachment device adapted to removably attach to the container neck and with a permanent retention strip around the container neck. The retention strip is adapted to pass, by folding, from a molding configuration to an operating configuration. A peripheral break line is then cut out in the skirt, adapted so as to be broken during the first opening of the plug. In some implementations, the retention strip may be prefolded and thereby pass from a molding configuration to an intermediate prefolded configuration. The retention strip is then folded until it passes into an operating configuration. In some implementations, the folding of the retention strip may pass the retention strip from an intermediate prefolded configuration to an operating configuration.