Outstanding Multispectral Radiation Shielding and Thermal Protection of Flexible Ultralight Core/Double‐Shell Fiber Composites

Next‐generation protection systems for medical, electronic‐device, and aerospace environments urgently require lightweight, flexible materials that protect the human body from multispectral radiation. However, simultaneously achieving strong broadband attenuation and effective thermal protection within ultralight fibrous structures remains a significant challenge. Here, a flexible ultralight core/double‐shell Bi/W 18 O 49 /GO/PAN fiber composite with thermal protection capability is developed. By constructing high‐Z W 18 O 49 /Bi double shells on electrospun GO/PAN fiber cores, the composite exhibits enhanced photon absorption together with efficient multispectral radiation blocking. It features an ultralow density of 0.40 g cm −3 , with <1% NIR‐Vis transmittance, 0.01% UV transmittance, and 95.46% attenuation of 33 keV X‐rays (µ/ρ = 17.12 cm 2 g −1 ). Benefiting from the synergistic barrier effect of the hierarchical porous fiber framework and the inorganic shell layers, the composite exhibits a remarkable heat‐insulating impact (ΔT = 43.9°C at 80°C), a low thermal conductivity of 33.5 mW m −1 K −1 , and a heat‐resistant temperature as high as 284°C. In addition, the composite demonstrates high mechanical stability, maintaining outstanding structural integrity and stable shielding performance even after 3000 bending cycles. This work provides a promising platform for advanced multispectral protection in complex, real‐world radiation environments.