In the present study, porous composite foams made of silicon rubber (SR), graphene nanoplatelets (GnP), and nickel ferrite (NiFe2O4) nanoparticles were developed using the salt template approach. SR act as a 3D porous network, the conductive channel provided by graphene nanoplatelets and the magnetic and dielectric loss provided by the NiFe2O4 and the composite foam as a whole showed absorption-dominated EMI shielding due to synergism between GnP and NiFe2O4. Without NiFe2O4, the total EMI SE is 23 dB, while different NiFe2O4 weight percentages (0%, 3%, 6%, & 9%) increase the SET up to 36.7 dB. The thermal conductivity of this prepared sample is found to be 0.0313 Wm−1K−1 for 9 wt% filler content of NiFe2O4. It shows a moderately low value as compared to existing polymer composites. The resulting SR/GnP@NiFe2O4 composite foams, which are lightweight, strong, and multifunctional, have straightforward synthesis procedures and have a myriad of possible uses for EMI shielding systems and thermal insulations in the disciplines of aerospace, military engineering, electrical engineering and electronics.