Fine-porosity glass foam was made from ground recycled waste glass, using sodium hydroxide dissolved in distilled water, borax, and titanium dioxide as additives. The dry mixture was heated for sintering at 810-825℃ in a constructively and operationally adapted microwave oven, heating times being varied between 27-60 min. The proportion of NaOH was increased from 4.5 to 9%, so that the NaOH/borax ratio had values between 0.75-1.50. The experiments allowed the identification of the optimal NaOH/borax ratio (1.25), so that the characteristics of the appropriate specimen were: density of 0.14 g·cm-3, porosity of 89.6%, heat conductivity of 0.042 W·m-1·K-1, and compression strength of 1.2 MPa. The pore size was very low (between 40-80 µm), obtaining a structure with predominant closed-porosity.