The research presents the method of effective EMR absorbing materials fabrication using glass microspheres (GMs) and ascertains the influence of GMs size, its content in the composite, and type of the nanocarbon admixture on the electrodynamic characteristics of the developed composites. It is revealed that EMR shielding efficiency of composite materials (CMs) with GMs of 100–200 μm diameter in the epoxy resin matrix filled with nanocarbon particles is the highest among the tested CMs: CMs with 5 wt.% of GNPs demonstrate the EMR shielding of 13.6 dB at \(R\) = 0.71 and \(A\) = 0.25 while the correspondent values for CMs with 3 wt.% of CNTs are 9.8 dB, 0.48, and 0.41. It was shown that the increasing content of GMs in the epoxy/nanocarbon CMs results in the decrease of EMR shielding characteristics. It is associated with a virtual decrease in the nanocarbon content in the CMs and indicates the dominant contribution of the nanocarbon component (graphite nanoplates carbon nanotubes) into the EMR attenuation. The modeling of the absorptive efficiency of the developed CMs shows that the positioning and depth of \({RL}_{min}\) depend on both the phase composition of the CMs and the thickness of the sample: an increase in the CMs complex dielectric permittivity and the sample thickness shifts \({RL}_{min}\) to a lower frequency and reduces the EMR absorption bandwidth.