Conductive polymer composites have become alternative materials for providing electromagnetic and electrostatic shielding where metals are not suitable. Polymer composites prepared with carbon nanomodifiers are corrosion-resistant, light-weight, and easy to process. Moreover, due to their nano-scale, nanocomposites can be shaped into thin-walled forms such as micro-injection molded or micro-textured extruded parts and films. The composite community has devoted considerable effort to the study and development of such composites for enhanced electrical conductivity. However, the electromagnetic shielding effectiveness (EM SE) of composites consisting of carbon nanomodifiers with medium to high concentrations has not been thoroughly examined. Therefore, in this study, the effect of crystallinity, morphology, concentration and orientation of carbon nanomodifiers on the shielding provided by their polyethylene-based composites has been investigated relative to their transport properties.