The paper gives the results a theoretical and experimental study of human made composite media in the form of a rubber–like material with rigid compact spherical or cylindrical inclusions. It is shown that in contrast to rubber–like materials with voids, which can be described by a complex compressibility, materials with solid compact inclusions can be described by a complex density. On the basis of a material with inclusions of spherical shape, the example is given of the synthesis of a wideband absorber whose properties are practically independent of the static pressure.