Glass breaks when stressed. There are five types of stress which may cause glass breakage:
1. thermal stress – from absorption of solar radiation.
2. tensile stress – from the weight of the glass itself.
3. mechanical flexing stress – from wind.
4. impact stress – from flying objects, hail, baseballs.
5. twisting stress – from building or window frame sagging or settling.
The first type, thermal stress, is the only one which film may affect. The use of window films will increase the thermal stress on sunlit glass. However, there are also other factors which will increase thermal stress such as: partial shading of windows from overhangs, tightly fitting drapes or blinds, signs or decals on windows, heating and cooling vents directed at glass. In addition, different types of glass (annealed versus tempered, clear versus tinted) have different solar absorption rates and will withstand different degrees of thermal stress.
The window film manufacturers have recommended film-to-glass tables for use by factory-trained dealer installers. If a consumer is ever in doubt, he/she should request a copy of such guidelines. Listed below are some glass types or conditions where the use of a solar control (not clear safety) type of window film is not recommended without extreme caution.
single pane glass larger than 100 square feet.
double pane glass larger than 40 square feet.
clear glass thicker than 3/8 inch.
tinted glass thicker than 1/4 inch.
window framing systems of concrete, solid aluminum, or solid steel .
glass where sealant or glazing compound has hardened.
visibly chipped, cracked or otherwise damaged glass.
reflective, wired, textured, or patterned glass.
triple pane glass.
laminated glass windows.