The construction starts from certain typical effective medium approximations for conductivity of idealistic isotropic matrix composites with randomly oriented inclusions of perfect spherical, platelet, and circular fiber forms, which obey Hashin–Shtrikman bounds over all the ranges of volume proportions of the component materials. Equivalent inclusion approach is then developed to account for possible diversions, such as non-idealistic geometric forms of the inhomogeneities, imperfect matrix-inclusion contacts, filler dispersions, and when the particular values of the fillers’ properties are unspecified, using available numerical or experimental reference conductivity data for particular composites. Illustrating applications involving experimental data from the literature show the usefulness of the approach.