Ultrathin, Stretchable, and 3D‐Printable Complementary Nanotubes–Polymer Composites for Multimodal Radiation Shielding in Extreme Environments

ABSTRACT A novel material system capable of simultaneously attenuating electromagnetic interference (EMI) and neutron radiation, while retaining multifunctionality such as lightweight and mechanical stretchability, is urgently needed for versatile passivation platforms in advanced aerospace, defense, medical, and next‐generation electronic applications operating under extreme environments. Here, we report (1) a neat composite comprising complementary nanotubes (boron nitride nanotubes, BNNTs, and single‐walled carbon nanotubes, SWCNTs) for dual‐mode attenuation that includes EMI and neutron shielding, and (2) its extension into a 3D‐printed architecture using an intrinsically stretchable polydimethylsiloxane (PDMS) matrix, which altogether enables a robust and conformable shielding architecture for emerging applications. Utilizing direct ink writing, we achieve scalable fabrication of structurally complex geometries (e.g., freestanding honeycomb lattices) with tunable mechanical and shielding properties. The resulting neat composites demonstrate EMI shielding effectiveness exceeding 50 dB and neutron attenuation coefficient of 1.27 mm −1 (equivalent to ∼72% attenuation at a mm thickness) at thicknesses on the order of tens of micrometers, where the polymer composites exhibit the shielding effectiveness up to 23 dB at sub‐millimeter thicknesses while maintaining mechanical resilience under cyclic strain and thermal extremes (–196°C to 250°C). These findings present a lightweight and robust shielding strategy for next‐generation electronics in harsh environments.