Lightweight Bismuth‐Based Liquid Metal Composite

Bismuth (Bi)‐based liquid metals exhibit stable solid states at ambient conditions and efficient solid–liquid transitions at relatively low temperatures, enabling simplified encapsulation and easier modification compared with conventional room‐temperature liquid metals. However, their relatively high density imposes limitations in weight‐sensitive fields such as wearable devices, biomedical implants, or robotic systems. Here, this challenge is addressed by introducing hollow glass microspheres into a Bi‐based liquid metal alloy, developing a lightweight Bi‐based liquid metal composite (BLMC). The resulting composite demonstrates a density reduction exceeding 50% while maintaining excellent electrical conductivity, thermal performance, and mechanical strength. The embedded microspheres also impart a granular microstructure, significantly enhancing the material's plasticity and enabling improved structural support and stiffness tuning when used as fillings or coatings. Practical demonstrations highlight the applicability of BLMC as injectable bone cement, wearable device coatings, and thermally responsive shape‐memory materials. Additionally, finite element modeling provides insights into the microscale interactions between microspheres and alloy, elucidating stress distributions and heat transfer characteristics within the composite. Overall, this work holds promise for extending the application scope of bismuth‐based liquid metals, paving the way for developing lightweight, multifunctional alloys suitable for wearable and intelligent material systems.