This invention relates to an endwall for a container having a panel portion surrounded by a substantially vertical wall portion which terminates into a narrow rim. The rim is connected to a sidwall of the container. The wall portion extends outward from the container and is adapted to be reformed inwardly into the container in a controlled manner by an external mechanism to reduce the volume thereof after the container has been filled and sealed. The invention also relates to a method of packaging a product in a container having a body opened at one end and closed at an opposite end by an endwall as described above. The method includes the steps of filling the container with a product and sealing the open end, thermally treating the filled and sealed container, and reforming the endwall inwardly into the container. The sequence of steps can be rearranged.