Abstract: The invention relates to a cap element adapted for being fixed to a container, which container comprises an upper surface that is bounded by an edge. The cap element comprises a one-piece, substantially rigid main cap that defines an interior space and at least one opening defined by a circumferential edge adapted to engage over the edge of the container so as to enclose at least part of the container, and sealing means in the interior space near the opening, within the circumferential edge of the main cap, which sealing means are adapted to engage against the upper surface of the container. At least one resilient fixing element is provided in the interior space near the opening, within the circumferential edge of the main cap, which resilient element is adapted to engage against or around the container edge.