The article presents the results of the development of the technology for manufacturing flexible microwave absorbers, the fillers of which are powdered activated coconut charcoal and moisture-containing ceramsite, and the matrix for these materials' particles holding is polyurethane mastic. The results of the study of the regularities of the electromagnetic radiation interaction in the frequency range of 0.7-17.0 GHz with absorbers, manufactured according to the developed technology, depending on the size of the ceramsite particles contained in them, are presented. On the basis of these results, it was found that the studied absorbers, in comparison with absorbers, filled with moisture-containing ceramsite, are characterized by lower values of the electromagnetic radiation reflection coefficient in the frequency range of 0.7-17.0 GHz, reaching a value of -20.0 dB. In this case, the values of their electromagnetic radiation transmission coefficient in the indicated frequency range reach the value of -43.0 dB. Microwave absorbers, manufactured according to the developed technology, are promising for use in order to solve problems related to ensuring the functional reliability of radio electronic equipment, as well as ensuring environmental safety and information security.