Abstract: The thermal conductivity of polymer composites filled with hollow microspheres is closely related to the content and structure of hollow microspheres. In this paper, micron-sized monodisperse polystyrene (PS) microspheres are synthesized as the sacrificial template to prepare a series of hollow SiO₂ (H-SiO₂) microspheres with different inner and outer radius ratios (r/R).The r/R value is controlled by the relative content of PS microspheres and tetraethyl orthosilicate (TEOS). The chemical composition and morphology of H-SiO₂ microspheres are characterized by infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. Further, H-SiO₂ microspheres are blended with polydimethylsiloxane (PDMS) at a certain content to obtain H-SiO₂/PDMS composite rubbers. The effect of the content and the r/R value of H-SiO₂ microspheres on the thermal conductivity of the composite rubber are investigated.Combined with the theoretical model calculation on the thermal conductivity of the silicone rubber,it can be concluded that the addition of H-SiO₂ microspheres with a complete hollow structure and an r/R value higher than 0.963 can reduce the thermal conductivity of H-SiO₂/PDMS composite rubbers.The more the H-SiO₂ microspheres, the smaller the thermal conductivity of the composite rubber.At the same time, when the mass fraction of H-SiO₂ microspheres is no more than 5%, the mechanical properties of the H-SiO₂/PDMS composite rubber are also enhanced with the increase of the weight content of H-SiO₂ microspheres. This work provides theoretical and experimental guidance for the design and preparation of high-performance hollow microspheres filled with polymer thermal insulation materials.