The invention relates to a valve plug (1) for sealing a container opening, comprising a valve body (2) that can be placed on the container opening and is made of a first, rigid plastic material and a valve element (3) that is integrally connected to the valve body (2) and made of a second, elastic plastic material, which is more elastic than the first plastic material, wherein the valve element (3) has a sealing surface section (6) that can be placed in a sealing manner on a contact edge and a connecting part (8), which extends from the sealing surface section (6) radially through an opening in the valve body (2) to a retaining section (10) held on the outer circumference of the valve body, wherein the sealing surface section (6) is held by the connecting part without axial support of the sealing surface section (6).