A septum for use in an implantable pulse generator. The septum includes a soft sealing material and a hard inner portion or core having a set of lips. The lips are exposed outside the soft sealing material and act to displace the sealing material when a force is applied, for example from a tool used to tighten or loosen a set screw, enlarging a slit, seam or slot into a passageway through the septum.
