Preparation and characteristic of a temperature resistance buoyancy material through a gelcasting process

•A temperature resistance composite with borosilicate glass as matrix was prepared.•The composite exhibited excellent mechanical and thermal properties.•The exponent m value was lower than that of open- or closed-cell foams.•Thermal conductivity value was close to that of Landauer’s relation prediction.•Young’s modulus agreed with Ashby–Gibson model for a porosity from 65% to 89%.