Tempered glass is a type of glass with evenly distributed compressive stresses on the surface which is made by heating float glass to nearly softening point and then cooling it down rapidly by air. During the instant cooling process, the glass exterior is solidified due to rapid cooling while the interior of glass is cooled down relatively slowly. This process will improve the glass exterior compressive stress and interior tensile stress resistance which can improve the overall mechanical strength of glass by gemination and result in good thermal stability.