Countless times I have heard consumers comment that the "glass guy" told them that window film causes seal failure in windows. Seal failure occurs when the sealant between the two panes of glass breaks, subjecting the airspace to the surrounding environment. Since the seal acts as the moisture barrier, if the seal breaks, condensation can develop in the airspace of the insulating glass window, making it look cloudy or filled with moisture droplets.
The environment inside an insulating glass unit can be affected by its external environment such as temperature and air pressure. Changes in temperature and air pressure put additional stress on the seals. The use of less resilient sealants in the construction of the insulating glass unit can also cause the seals to fail. Most manufacturers, however, design and test their products to withstand significant changes in air pressure and temperature, thereby reducing the chance of failures. Nevertheless, seal failure does and will continue to occur simply because of the way in which insulated units are manufactured, shipped and installed. In fact, the insulating glass manufacturers association (SIGMA) has found normal seal failure to be at a rate of 1.5% of the insulated units.
So, does window film cause seal failure? Not likely. The window film industry has conducted a number of tests to evaluate the affect of window film on sealed glass units. Results indicate that on a clear insulating unit, window film designed for residential and commercial application only increases the summertime airspace temperature by no more than 22 degrees, a pressure increase of only .55 psi (pounds per square inch). Put into perspective, most manufacturers of the glass units design their products to withstand a pressure change of 3.30 psi, over six times the film's potential pressure increase.
What can you do? We advise our customers who have seal failure concerns to contact their window manufacturer. If your window manufacturer voids the warranty on the window when film is installed, you should ask for their test data supporting these warranty limitations.