Conventional adhesives often encounter interfacial failure in humid conditions due to small droplets of water condensed on surface, but spider silks can capture prey in such environment. Here a robust spider‐silk‐inspired wet adhesive (SA) composed of core–sheath nanostructured fibers with hygroscopic adhesive nanosheath (poly(vinylpyrrolidone)) and supporting nanocore (polyurethane) is reported. The wet adhesion of the SA is achieved by a unique dissolving–wetting–adhering process of core–sheath nanostructured fibers, revealed by in situ observations at macro‐ and microscales. Further, the SA maintains reliable adhesion on wet and cold substrates from 4 to −196 °C and even tolerates splashing, violent shaking, and weight loading in liquid nitrogen (−196 °C), showing promising applicability in cryogenic environments. This study will provide an innovative route to design functional wet adhesives.

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Nanoparticle aggregation for constructing functional materials has shown enormous advantages in various applications. Most efforts focused on ordered nanoparticle aggregation for specific functions but were often limited to irreversible aggregation processes due to the thermodynamic equilibrium. Herein, we report a reversible disordered aggregation of SiO2‐PNIPAAm nanoparticles (SPNPs) through thermo‐responsive jamming, obtaining smart liquid–solid switchable materials. The smart materials can display a switch between liquid‐like state and solid‐like state responding to a temperature change. This unique macroscopic behavior originates from the reversible disordered aggregation modulated by temperature‐dependent hydrophobic interactions among the SPNPs. Notably, the materials at the solid‐like state show anti‐impact properties and can withstand the impact of a steel sphere with a speed of 328 cm s−1. We envision that this finding offers inspiration to design smart liquid–solid switchable materials for impact protection.