There is a myth making the rounds that window film causes seal failure in multi-pane insulated glass window units. At first glance, the myth makes sense. It’s based on two truths. However, for the myth to not fall apart you must ignore two other truths and never actually research to see if anyone has put the myth to the test.


The Myth

For a myth to gain a foothold, it has to have some internal logic. If it doesn’t make sense, no one would believe it. This myth begins with two true statements.

1. When applying window film to insulated windows, the film goes on the interior side of the unit. 2. As the weather warms up, the film reflects heat back through the unit.


Based on this, the myth then says that the interior gasses trapped in the unit will expand and contract as the temperature rises and falls, causing the unit to swell and constrict, breaking the seals and causing the unit to fail. Unfortunately for the myth, this ignores two facts.


The Facts

First, even without window film reflecting heat back, the units warm and cool as the weather changes – and the gasses inside expand and contract. This is how they were designed. Second, even a 20-22 F degree increase (unusual for most films) will result in a less than 3% change in air pressure, whereas properly made units are designed and tested to withstand 22% changes in air pressure*.


For some, this simple math is enough to explain why in over 30 years of observation** we have never witnessed an increase in failure rates for units with film versus units without. But why stop there, when we can find out once and for all?


The Test

The Window Film Committee of the Association of Industrial Metallizers, Coaters, and Laminators (AIMCAL) commissioned A. William Lingnell, P.L., a technical consultant to SIGMA, to conduct the standard ASTM tests (E773 and F774) on standard sealed units with and without window film.


These test were conducted by A. William Lingnell (B.S. Civil Engineering, M.S. Civil Engineering, M.S. Mechanical Engineering, M.S. Engineering Science) of Lingnell Consulting Services, the technical consultant to the Sealed Insulating Glass Manufacturers Association (SIGMA). He has over 30 years of experience in the technical field of glass and architectural products and is considered one of the world’s foremost experts in the field. He is a member of American Architectural Manufacturers Association; American Association for Wind Engineering; American Society of Civil Engineers; American Society of Heating, Refrigerating, and Air Conditioning Engineers; American Society for Testing and Materials; American Welding Society; Association of Construction Inspectors, Building Officials and Code Inspectors; Construction Specifications Institute; International Conference of Building Officials; National Fenestration Rating Council; National Fire Protection Association; National Glass Association; National Society of Professional Engineers; and Southern Building Code Congress International.


Conclusion: Based on the testing conducted on these units, window film had no observable effect on the performance of high quality manufactured insulated units.


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All dual pane windows will suffer from seal failure at some point, with the cheaper windows failing sooner than better quality ones. The likelihood and frequency of seal failure is primarily determined by the quality of workmanship and the materials used to build the insulated glass units. Your best protection against seal failure is to buy well-made units from a reputable window manufacturer***.


If you are the orginal homeowner and you are still under your window manufacturer’s window warranty, 3M will automatically give you 40 months of seal failure protection from the date of installation, not to exceed any window manufacturers warranty. If your warranty goes beyond the 40 months an extended warranty is available @ .35 cents per sqft. which covers your window manufacturer’s warranty.







*Results indicate that residential film only increases the summertime airspace temperature by no more than 22 degrees, a pressure increase of only .55psi (pounds per square inch). Put into perspective, most manufacturers of insulating glass units design their products to withstand a pressure change of 3.30 psi, over six times the film’s potential pressure increase! Source:



**A longevity study conducted by SIGMA which started in 1980, found that sealed unit designs which passed the highest level of performance testing failed at a rate of approximately 4% over 15 years. Units passing lower levels of performance failed at a rate of approximately 10% over 15 years. Sealed unit design has improved significantly since 1980 and SIGMA estimates that current high performance units may have a failure rate as low as 1% if all three of the major reasons for seal failure are eliminated. While 1% may seem like a low number it still means 1 in every 100 sealed units will fail before the warranty period. Source: Click here


***Source: Click here