Glass breaks when stressed. There are five types of stress, which may cause glass breakage:
Thermal Stress—from absorption of solar radiation.
Tensile Stress—from the weight of the glass itself.
Mechanical Flexing Stress—from wind.
Impact Stress—from flying objects, hail, baseballs.
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, and 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.
Our 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 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:
Any single pane glass larger than 100 square feet
Dual pane glass larger than 40 square feet
Clear glass thicker than 3/8 inch
Triple or quadruple pane glass
Window framing systems of concrete or metal that have no gaskets or seals
Glass where framing sealant or gaskets that are no longer resilient
Damaged, chipped, cracked or scratched glass
Round, bent, laminated, textured, wired glass or skylights