Photocuring‐Induced Interfacial Dielectric Transition for Absorption‐Dominated Electromagnetic Interference Shielding in Multi‐Material <scp>3D</scp> ‐Printed Composites

ABSTRACT Although multilayer electromagnetic interference (EMI) shielding composites can effectively enhance electromagnetic attenuation, the influence of photocuring‐induced interfacial regions in multi‐material additive manufacturing remains fundamentally unclear. Herein, we report an interfacial dielectric transition strategy for achieving absorption‐dominated EMI shielding in multi‐material vat photopolymerization (VPP) 3D‐printed CNT/polymer composites. Alternating insulating/conductive multilayer architectures were fabricated to manipulate electromagnetic wave propagation and internal reflection behavior. More importantly, a photocuring‐induced interfacial layer with an effective thickness of approximately 0.2 mm was identified between adjacent layers, generating a gradual dielectric transition from insulating to conductive domains. This interfacial transition substantially improved impedance matching and promoted electromagnetic energy dissipation within the multilayer structure. As a result, the optimized (In/Con) 5 structure achieved a shielding effectiveness (SE) of 35.05 dB, with absorption contributing over 93% of the total shielding performance. Electromagnetic simulations incorporating the interfacial transition layer exhibited excellent agreement with experimental results, confirming the critical role of interface‐regulated wave attenuation. The findings reveal that photocuring‐induced interfaces should be regarded as functional electromagnetic units rather than fabrication artifacts, thereby establishing a universal structure–interface coupling paradigm for designing lightweight and absorption‐efficient EMI shielding composites.