Thermally reduced graphene networks (TRGN) with low densities, less than 10 mg cm⁻³, were synthesized by thermal reduction of graphene oxide/poly(vinyl alcohol) networks. To evaluate the electromagnetic wave absorption properties of TRGN, TRGN were nondestructively backfilled with wax via a vacuum-assisted method. The as-prepared TRGN/wax composites, using integrated TRGN as fillers rather than directly dispersing graphene sheets in wax, exhibit better electromagnetic wave absorption capabilities because of the 3D conductive frameworks, which could generate more effective electrical loss in terms of dissipating the induced current in the TRGN/wax composites. Specifically, for the TRGN/wax composite with ∼1 wt% TRGN, the minimum reflection loss reaches −43.5 dB at 12.19 GHz with a thickness of 3.5 mm, and the bandwidth of reflection loss less than −10 dB (90% absorption) can reach up to 7.47 GHz. More importantly, our work provides a promising approach for constructing graphene-based composites with strong electromagnetic wave absorption ability at very low filler loadings.