Abstract: An improved membrane-type end closure member for composite containers or the like is disclosed, characterized in that the end closure member is deformed to define an annular deformation of generally V-shaped or flat bottom transverse cross-section, which deformation extends partially within the end of the container when the end closure member is bonded to the open upper end of the container body. The annular deformation, which is arranged between the annular flange portion that is bonded to the end extremity of the container and a central circular disk portion of the end closure member, serves to reinforce the relatively thin flexible membrane member and flexes or "domes" in response to variations in internal pressure of the container to maintain the container in a closed condition.