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In this work, a composite of barium ferrite (BaM) and multiwalled carbon nanotubes (CNTs) in a polymer matrix of polydimethylsiloxane (PDMS) are reported for the purpose of suppressing electromagnetic interference (EMI). Shielding is accomplished primarily through absorption, which arises from a combination of the ferromagnetic resonance (FMR) from the BaM and conductive losses from the CNTs. The composite is fabricated by mixing commercially available BaM nanoparticles and CNTs into PDMS, screen printing the mixture into molds, then curing at 80 °C in a DC magnetic field. Characterization involves placing the composite in the cross‐section of a rectangular waveguide, then using a vector network analyzer (VNA) to measure scattering (S) parameters from 33–50 GHz. Using the measured S parameters, power reflected and absorbed can be calculated and used to characterize the composite's shielding effectiveness (SE), and the complex permittivity and permeability can be determined. The resulting 2.4 mm thick composite shows a peak absorption of 26.9 dB at the FMR frequency of 47.4 GHz. When normalized for thickness, the composite, on average, absorbs 11.3 dB mm⁻¹and operates at a higher frequency than other shielding composites found in the literature.