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Lightweight structural materials are commonly used as effective fillers for advanced composites with high toughness. This study focused on enhancing the toughness of direct‐spun carbon nanotube yarns (CNTYs) by controlling the micro‐textural structure using a water‐gap‐based direct spinning. Drawing inspiration from the structural features of natural spider silk fibroin, characterized by an α‐helix in the amorphous region and β‐sheet in the crystalline region, multiscale bundles within CNTYs are reorganized into a unique nano‐coil‐like structure. This nano‐coiled structure facilitated the efficient dissipation of external mechanical loads through densification with the rearrangement of multiscale bundles, improving specific strength and strain. The resulting CNTYs exhibited exceptional mechanical properties with toughness reaching 250 J g−1, making them promising alternatives to commercially available fibers in lightweight, high‐toughness applications. These findings highlight the significance of nano‐coiling engineering for emulating bio‐inspired micro‐textural structures, achieving remarkable enhancement in the toughness of CNTYs. [ABSTRACT FROM AUTHOR]

Super strong fibers, such as carbon or aramid fibers, have long been used as effective fillers for advanced composites. In this study, the highest tensile strength of 5.5 N tex−1 for carbon nanotube yarns (CNTYs) is achieved by controlling the micro‐textural structure through a facile and eco‐friendly bundle engineering process in direct spinning without any post‐treatment. Inspired by the strengthening mechanism of the hierarchical fibrillary structure of natural cellulose fiber, this study develops multiscale bundle structures in CNTYs whereby secondary bundles, ≈200 nm in thickness, evolve from the assembly of elementary bundles, 30 nm in thickness, without any damage, which is a basic load‐bearing element in CNTY. The excellent mechanical performance of these CNTYs makes them promising substitutes for the benchmark, lightweight, and super strong commercial fibers used for energy‐saving structural materials. These findings address how the tensile strength of CNTY can be improved without additional post‐treatment in the spinning process if the development of the aforementioned secondary bundles and the corresponding orientations are properly engineered. [ABSTRACT FROM AUTHOR]