PURPOSE: To obtain a heat-insulating glass having high infrared reflectivity, by substituting sodium in the surface layer of glass with potassium, reheaing the glass, and coating the product with metal oxide.

CONSTITUTION: Sodium ions existing in the glass surface layer at about 25W 40μm in depth are substituted with potassium ions e.g. by immersing a soda lime-silica glass in potassium nitrate bath at about 460°C. The treated glass is reheated at ≥550°C, and coated with a coating layer by spraying a metallic compound such as dibutyltin oxide free of fluorine to the surface. By this treatment, the pollution problem of the oxide coating layer with sodium migrated from glass can be solved, and a high quality coating layer having high infrared reflectivity can be formed.