Low Thermal Conductivity Materials: From Fundamentals to Applications

ABSTRACT Low thermal conductivity (K) materials are central to energy saving, thermal management, and extreme‐environment protection. Recent advances in aerogels, polymers, porous ceramics, composites, and architected materials have greatly expanded the design space for high‐performance thermal insulators. This review summarizes the latest progress toward the ultimate thermal insulator from the perspective of heat transport regulation, with emphasis on suppressing solid conduction, gas conduction, and thermal radiation through multiscale structural engineering. Key material systems and design strategies are highlighted, together with the structure–property relationships governing ultralow thermal conductivity. Current challenges in mechanical stability, environmental durability, scalability, and practical deployment are also discussed. This review provides a concise framework for understanding the mechanism, recent developments, and guiding the design of next‐generation thermal insulating materials.