A closing valve for a container for a fluid includes an outer jacket connected or connectable to an opening in the container or forming part of the container. An inner jacket is accommodated inside the outer jacket and has an opening through which the fluid can be fed to or withdrawn from the container. A closing element is positioned inside the inner jacket or between the inner jacket and the outer jacket and movable between at least a first position closing the opening and a second position clearing the opening, wherein at least the closing element is made from a polymer material. The closing element comprises a sealing member and a spring, which urges the closing element into the first position.