Abstract: The present invention relates to a closure or cap for a container containing a fluid. The closure or cap is characterized in that the slotted structure comprises several pivoting plates hinged to the body in such a way as to be able to pivot; at least one pivoting plate, preferably each pivoting plate, being connected movably to a neighbouring pivoting plate via a cross section of more flexible deformation than the several pivoting plates, which forms one of the free terminal edges of the slot or slots and is, in a condition of actuation without overpressure inside the container, arranged basically contiguously with the other free terminal edge situated opposite the slot or slots and can open by pivoting away from the inside of the container when the fluid generates increased pressure inside the container, whereupon it moves away from the other free terminal edge.