A closing cap for a container comprising: - an outer shell which extends along a longitudinal axis (X) and comprises a lateral wall , which extends about the axis (X), in particular having a shape which is tubular and coaxial with the axis (X), and an end wall (302; 317), which closes the lateral wall at one end for delimiting a concavity; wherein the lateral wall is internally provided with a coupling structure , configured for removably coupling the cap to a neck of the container in such a way that the cap is movable from a closing position, in which the cap closes a mouth of the container , to an opening position; - an inner component (4; 4') positioned for closing the mouth of the container , when the cap is in the closing position, comprising a closing element provided with an inner portion (401; 401'), which is configured, in use, for facing the mouth , and an outer flange , extending externally relative to the inner portion (401; 401'), which is configured for fixing to the outer shell ; - a chamber , suitable for containing a product (P) intended to be supplied into the container through the mouth , which is at least partly delimited by the inner portion (401; 401'); wherein the cap comprises an opening promoting assembly and the inner portion (401; 401') comprises a breakable portion , the opening promoting assembly being configured for axially stressing the breakable portion in such a way as to create a supplying outlet in the inner portion (401; 401') and to make the product (P) come out of the chamber , supplying the product (P) into the container through the mouth ; characterized in that the outer shell comprises a spacer wall , which extends from the end wall (302; 317) and is internally coaxial relative to the lateral wall , the spacer wall being configured for making contact with the closing element and for spacing the latter from the end wall (302; 317) defining a free space between the end wall (302; 317), the spacer wall and the closing element . - an outer shell which extends along a longitudinal axis (X) and comprises a lateral wall , which extends about the axis (X), in particular having a shape which is tubular and coaxial with the axis (X), and an end wall (302; 317), which closes the lateral wall at one end for delimiting a concavity; wherein the lateral wall is internally provided with a coupling structure , configured for removably coupling the cap to a neck of the container in such a way that the cap is movable from a closing position, in which the cap closes a mouth of the container , to an opening position; - an inner component (4; 4') positioned for closing the mouth of the container , when the cap is in the closing position, comprising a closing element provided with an inner portion (401; 401'), which is configured, in use, for facing the mouth , and an outer flange , extending externally relative to the inner portion (401; 401'), which is configured for fixing to the outer shell ; - a chamber , suitable for containing a product (P) intended to be supplied into the container through the mouth , which is at least partly delimited by the inner portion (401; 401'); wherein the cap comprises an opening promoting assembly and the inner portion (401; 401') comprises a breakable portion , the opening promoting assembly being configured for axially stressing the breakable portion in such a way as to create a supplying outlet in the inner portion (401; 401') and to make the product (P) come out of the chamber , supplying the product (P) into the container through the mouth ; characterized in that the outer shell comprises a spacer wall , which extends from the end wall (302; 317) and is internally coaxial relative to the lateral wall , the spacer wall being configured for making contact with the closing element and for spacing the latter from the end wall (302; 317) defining a free space between the end wall (302; 317), the spacer wall and the closing element . <EOS>