The recent surge in the usage of electronics has led to a new kind of problem; electromagnetic interference which necessitates finding alternate materials that offer ease of processing, design flexibility, light weight, and ease of embedding and integrating with the existing systems in place as shields to protect the precise electronic circuitry. Herein, lightweight polycarbonate (PC)-based nanocomposites using doped graphene derivatives and multiwalled carbon nanotubes (MWCNT) has been explored for effective shielding of EM radiation in X- and Ku-band. To get a mechanistic insight as to how the dopant in graphene derivatives influences the EM shielding properties, two dopants have been explored here: ferrimagnetic (ferrite, Fe 3 O 4 ) and the other one as paramagnetic (gadolinium oxide, Gd 2 O 3 ). The doped graphene derivatives when composited with PC and MWCNTs resulted in materials that can shield the incoming EM radiation through magnetic and dielectric losses. This strategy of doping improves the state of dispersion of these dopants in the nanocomposites, besides enhancing the shielding effectiveness. The PC-based nanocomposites illustrated a total shielding effectiveness (SE T ) of -28 and -33 dB at 18 GHz for a given concentration of Gd 2 O 3 and Fe 3 O 4 hybrid, respectively. A closer look into the mechanism of shielding reveals that irrespective of the dopant, various losses (magnetic and dielectric) decide the shielding effectiveness in polymeric nanocomposites facilitated by multiple internal reflections. Taken together, this study brings in new insight as to how the losses contribute toward effective shielding rather than the choice of the dopant and will help guide researchers working in this area from both industrial as well as academic perspective. Copyright © 2019 American Chemical Society.