Advances in foam-based materials for electromagnetic interference shielding: synthesis, properties, and performance.

Electromagnetic pollution has intensified with the rapid expansion of wireless technologies and compact electronics. This has created a high demand for lightweight materials that can absorb microwaves (MA) and shield against electromagnetic interference (EMI). Foam-based structures are promising options because their porous designs naturally match impedance, promote internal reflections, and enable various loss mechanisms. These structures are also very light. Recent fabrication methods, such as freeze casting, space-holder replication, 3D printing, sol-gel foaming, and bio-templating, allow precise control over pore size, anisotropy, and the formation of conductive or magnetic networks. This enables customization of shielding performance. This review offers an integrated assessment of various foams, including metal, carbon, polymer, composite, and hybrid types. It examines how pore shape, interfacial properties, and filler connectivity influence conduction loss, interfacial polarization, magnetic interactions, and absorption-based attenuation. A major contribution is the systematic comparison of specific shielding effectiveness-measured as SE per density and SE per density-times-thickness-across representative systems. These comparisons show that optimized foam structures can outperform dense materials on a weight basis. This advantage is especially important for aerospace, wearable electronics, and portable devices. The review also highlights persisting challenges, including limited structure-property models, thermochemical instability, and measurement artefacts in ultralight foams. Finally, it outlines three promising research paths; biodegradable foams, magnetically tunable hybrids, and impedance-graded architectures, positioning foam-based materials as strong candidates for next-generation, sustainable EMI shielding.