[en] In the lecture the problem of application of very cold neutrons in solid state physics is treated. The work on the production of very cold neutrons at the FRM reactor is described together with their application to the investigation of inhomogeneities in solids and for total cross section measurements. The experiments on neutron containment in graphite neutron bottle are described. The data obtained suggests that electrographite (and other inhomogeneous materials like hot - pressed beryllium of BeO) might be useful as efficient reflectors around Converters in beam tubes for relatively fast very cold neutrons in the velocity range up to about 50 m/s