Resistance To Thermal Stress
(Thermal Breakage)

Glass like most other materials expands with the increase in temperature. When glass is directly exposed to solar radiation, it absorbs heat, rises in temperature and expands. The edges of the glass in the frame, which are shielded from the radiation, remain cooler than the exposed area. The force generated by the expansion of the central portion of glass stretches the cooler edges and causes stress which, should it reach the breaking stress of the glass, will result in thermal breakage.