The electromagnetic interference (EMI) shielding properties of polycarbonate/graphene composites foamed with supercritical carbon dioxide were investigated as a function of cellular morphology and graphene particle dispersion. The 2-step foaming method used was found to improve graphene dispersion and led to a different cellular structure compared to traditional 1-step foaming. Reflection was found to be the dominant EMI shielding mechanism and EMI shielding effectiveness was improved with large cell morphology that promoted isotropic/random orientation of graphene particles. A maximum EMI specific shielding effectiveness of 78 dB·cm3/g was achieved in foams, which was more than 70 times higher than that of the unfoamed polymer(1.1 dB·cm3/g). The study shows that by controlling foaming process conditions and nanoparticle characteristics, it is possible to improve multiple properties while achieving lightweight materials suitable for various applications.