Carbon-based materials and metals are two of the most used materials for EMI shielding, as they combine high electrical conductivity and effective wave reflection. As non-conductive materials, polymers are less effective, unless when combined with other functional materials and/or components. Thanks to the improvements done in recent years on carbon-based nanofillers, namely in terms of industrial synthesis processes and control of their structure, their combination with polymers has been considered as a strategy to obtain conductive nanocomposites with enhanced EMI shielding efficiency. Researchers have recently considered creating lightweight components based on such nanocomposites through foaming, with the intention of further improving EMI shielding for the most varied applications, especially high performance sectors such as aerospace or telecommunications. Foaming has been shown to lead to even lighter structures and effectively reduce nanofillers’ electrical percolation threshold. Also, the creation of a microcellular structure may promote an absorption/multiple reflection EMI shielding mechanism, mitigating wave interaction with surrounding devices.

With all these ideas in mind, microcellular nanocomposite foams based on polysulfones and carbon-based nanofillers were prepared and characterized in terms of their EMI shielding performance. It was observed that the electrical conductivity of the foams, directly proportional to their EMI shielding efficiency, not only increased as expected with the addition of conductive graphene nanoplatelets (GnP), but also with reducing density, reaching values > 10^-2 S/m, enabling their use from ESD to EMI shielding applications. As a consequence, the resulting foams displayed increasingly higher EMI SE values with incrementing GnP’s amount, reaching specific values > 10 dB·cm³/g in the X-band frequency range (8-12 GHz). The addition of nanohybrids based on the combination of GnP and carbon nanotubes further enhanced the specific EMI SE of the microcellular foams up till 20 dB·cm³/g, with the additional advantage of promoting an absorption/multiple reflection main EMI shielding mechanism.