Disclosed herein is a pierceable elastic septum for use in drug reservoirs and infusion sets, the pierceable septum comprising a first surface and a second surface. The first surface and the second surface are positioned opposite to each other. A distance between the first surface and the second surface is not constant over the first surface, and is configured such that if a higher pressure is applied to the first surface as compared to the second surface, a component of a force, which is exerted on the first surface, acts towards an axis (A) which intersects the center of the first surface and the center of the second surface.
