It is described a mold to form caps closing containers, by compression molding doses of plastic material, wherein a bottom wall of the cap, or at least one part thereof, is very thin, said mold comprising two half-molds (1,2) being axially movable towards each other, which assume an end closed position, without dose, wherein a tubular element (3) being slidable around the second half-mold partially defines the cavity, the tubular element is arranged contacting an axial abutment (4) of the first half-mold (1) at one side and an axial end stop (8) of the second half-mold (2) at the other side, with the purpose of preventing the hard contact between the half-molds (1,2).