Multiscale Carbon‐Reinforced Thermoplastic Foam Composites for Tunable <scp>EMI</scp> Shielding and Robust Mechanical Strength

ABSTRACT Achieving high‐efficiency electromagnetic interference (EMI) shielding while maintaining robust mechanical integrity in lightweight materials remains a formidable challenge for advanced aerospace and electric aviation applications. Herein, a scalable thermal expansion molding strategy is proposed to fabricate hierarchical all‐thermoplastic EM/MWCNT/PE composite foams. This architecture synergistically integrates a multi‐walled carbon nanotube (MWCNT)‐functionalized closed‐cell porous core with continuous carbon fiber (CF) fabric reinforcements. The hierarchical structural design effectively transforms the material's failure mode from brittle fracture to resilient multidimensional energy dissipation, yielding a remarkable 443% enhancement in peak impact load‐bearing capacity and a high flexural strength of 26.82 MPa. Furthermore, the composite delivers an exceptional total EMI shielding effectiveness (SE T ) exceeding 100 dB and an outstanding specific SE of 255 dB cm 3 /g. Crucially, supported by experimental power coefficients and electromagnetic simulations, we demonstrate that by simply adjusting the placement of the CF layers (internal core vs. external skins), the EMI attenuation mechanism can be precisely customized from reflection‐first to deeply absorption‐dominated. This customizability is driven by a Fabry‐Perot‐like macroscopic resonance effect and optimized surface impedance matching. This unprecedented synergy of customizable electromagnetic attenuation and robust mechanical strength firmly establishes the hierarchical composite foam as a highly promising candidate for next‐generation lightweight structural enclosures.