An apparatus for a hearing instrument, the hearing instrument being configured to be at least partially placed in an ear canal of a wearer of the hearing instrument, the apparatus comprising: a sealing element configured to seal off the ear canal when the hearing instrument with the apparatus is at least partially positioned in the ear canal, wherein operation of the sealing element is controlled by an electric control signal, the sealing element being at least partially made from an electroactive material, wherein an acoustic impedance of the electroactive material of the sealing element varies as a function of an applied electric field, the applied electric field being based on a characteristic of the electric control signal.