Effect of Honeycomb Architectures on EMI Shielding ( EMI SE ) and Reflection Loss ( RL ) in Multi‐Material 3D ‐Printed Polylactic Acid ( PLA )

Fused filament fabrication (FFF) enables multimaterial architectures with functional properties, providing a scalable route to customizable electromagnetic interference (EMI) shielding with complex geometries. Commercial conductive PLA and neat PLA were printed as plate‐based structures, including dense plates and honeycomb‐core sandwich architectures with 10% and 20% infill. Filaments were characterized by FTIR, TGA, and DMA, while printed parts were analyzed by SEM and evaluated in the X (8.2–12.4 GHz) and Ku (12.4–18 GHz) bands. Dense conductive PLA parts exhibited low microwave absorption (RL ≈ −2.5 dB) due to impedance mismatch and dominant surface reflection, whereas introducing insulating PLA layers improved impedance matching and increased high‐frequency absorption. For honeycomb cores, 10% infill enhanced absorption through lower effective permittivity and increased multiple internal reflections, while 20% infill increased effective density/permittivity and reduced absorption. EMI shielding effectiveness (EMI SE) depended primarily on conductive‐skin thickness, conductive volume fraction, and core architecture, with conductive skins on both outer surfaces consistently outperforming insulating‐skin designs. Across all architectures, shielding was absorption‐dominated (SEA ≫ SER). The best balance between performance and material efficiency was achieved with 3 mm conductive skins and a 2 mm insulating honeycomb core at 10% infill, delivering ~23 dB EMI SE.