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• Development of low-density open- and closed-porous foamed glasses. • Homogeneous pore structure with >90% of open or closed pores. • Open porosity achieved by partial crystallization of the glass. • Low thermal conductivity (37.5–65.6 mW m−1 K−1) measured using heat-flow meter. • Analysis of the difference in the thermal conductivity. Future developments in foamed glass should focus on improving the thermal insulation properties, controlling the foamed structure and the type of porosity. In this study, we report on the synthesis and properties of foamed glasses with open-porous and closed-porous structures prepared from waste cathode-ray-tube (CRT) panel and soda-lime-silica glasses with the addition of carbon black, and manganese or iron oxides. The samples exhibit a homogeneous structure with an average pore size in the range 0.5–1.35 mm and open porosity above 91% or closed porosity above 92%. The open porosity was obtained by partial crystallization of the glass during the foaming process. The thermal conductivity, measured using a heat flow meter at 10 °C, is 57.2–65.6 mW m−1 K−1 at 116–143 kg m−3 for the open-porous samples and 37.5–56.2 mW m−1 K−1 at 107–245 kg m−3 for the closed-porous samples. The conduction in the solid phase contributes the major part to the effective thermal conductivity (52–72%). The conduction in the gaseous and solid phases, respectively, is higher in the open-porous foamed glass due to the different gas composition (air) and the different solid composition (glass composition and crystalline content). The developed foamed glasses also have high mechanical strength, making them suitable for load-bearing applications. [ABSTRACT FROM AUTHOR]