Hollow Glass Microsphere/Polymer Composites for Thermal Insulation: Mechanisms, Fabrication, and Performance‐Driven Multifunctional Expansion

ABSTRACT Thermal insulation materials play an important role in industrial thermal insulation and high‐end equipment. Traditional polymers often suffer from relatively high thermal conductivity, while highly porous polymers demonstrate insufficient mechanical properties. Hollow glass microspheres (HGMs) offer a solution with low thermal conductivity, high strength, low density, and robustness. This paper thoroughly reviews the factors and mechanisms influencing the intrinsic thermal conductivity of polymers, and details the fabrication methods of HGM/polymer composites. On this basis, the influencing laws of HGMs on the mechanical and thermal‐insulation properties of the composites are elucidated. Beyond conventional thermal insulation, this review extends its scope to embrace a wider spectrum of application‐oriented functionalities. Intrinsically, the hollow cavity structure not only suppresses heat transfer but simultaneously endows the composites with lightweight characteristics, acoustic absorption, and low dielectric properties representing inherent physical synergies. To meet the demands of specific service environments, the thermal insulation function is further integrated with flame retardancy, ablation resistance, and photothermal regulation. Critically, the application in underwater high‐pressure protection is highlighted as a paradigm of scenario‐driven design, where thermal retention must be synergistically balanced with superior hydrostatic pressure resistance and seawater corrosion resistance for deep‐sea engineering.