Abstract: A hearing aid device for processing sound, which comprises a device for transducing sound to an electrical signal, a device for processing the electrical signal, a device for powering and regulating the processing device, and a device for transducing the processed electrical signal into sound, all these devices being enclosed in a case adapted for being inserted in an ear canal, an elastic layer defining a chamber on the outside of the case, the chamber containing a cold-curing composition consisting of at least two components, at least one partitioning wall within the chamber for separating the components from one another, the partitioning wall being adapted to be ruptured by being subjected to a pressure effect, the components being adapted, when being combined upon rupture of said wall, to provide a composition which expands during an initial curing period, and then sets rigidly with a substantial form stability.