Abstract: An improvement to the plugs of bottles generally cylindrical in shape, delineated by a so-called upper end (4) and a so-called lower end (5). The cylindrical body (1) of the plug includes a cylindrical wall (6) made of moulded plastic material, inside which are provided—a sealing structure (20) at least liquid-proof, and—a stiffening honeycomb structure (7), also made of moulded plastic material, provided as single block with the cylindrical wall; the honeycomb structure (7) is formed of a plurality of longitudinal channels (10) juxtaposed, which channels (10) extend from the sealing structure (20) up to at least one of the upper (4) and/or lower (5) ends of the cylindrical body (1), at which they emerge, and it is in the form of a beehive structure, formed of channels, whereof at least the greater portion exhibits transversal hexagonal or substantially hexagonal section.