Abstract: The invention concerns a heat accumulator consisting of a vessel having a wall which is at least partially heat conducting, the vessel contains a material which exothermally absorbs and endothermally desorbs a heat transporting substance, the absorbing and desorbing material in particular being sodium sulphide and being adhered to the wall of the vessel by means of a fibrous material such as cellulose. Also provided is a process for the production of such a heat accumulator comprising, applying a fibrous material to the inner wall of a closeable vessel, preferably via conducting protrusions, and subsequently contacting the absorbing and desorbing material being in a molten and/or hydrated state with the fibrous material.