A method and apparatus (10, 10, 10a, 110) for filling an expandable in-ear device (1) having in-flow (11) and out-flow (13) canals including a plurality of pressurizable chambers (20a, 20b, 134) in which the components (A, B) of a settable polymer are held under high relative pressure. The component chambers (20a, 20b, 134) are connected to a common mixing element (21, 154) which mixes the components (A, B) before they are applied to the in-flow canal (11) of an in-ear device (1 ). A sealed relief chamber (25, 164) is connected to the out- flow canal (33) of the in-ear device (1) and receives excessive mixed compound as it exits the in-ear device (1). In one embodiment, the relief chamber (25) is in contact with the elastic membranes (19a, 19b) of the component chambers (20a, 20b) such that when the elastic membranes (19a, 19b) contract the pressure in the relief chamber (25) decreases, maintaining the pressure (P3) below a predetermined pressure level (P2).
