Window Film Blog
Photo of a double pane window for a blog post entitled Can You Install Window Film on Double-Pane Windows

Can you install window film on double-pane windows?

Can you install window film on double-pane windows? This is a question we get asked a lot because there is a persistent myth out there that you can’t install film on double-pane windows. Visit any social media account, Reddit or Quora chat forum about window film and inevitably someone will post a comment that you should NEVER install window film on double-pane windows.

We’re here to tell you that this is not true. You can install window film on double-pane windows, but there are some considerations to keep in mind. 

Let’s start by explaining what a double-pane window is…

What is a double-pane or dual-pane window?

Double-pane windows, also known as dual-pane or double-glazed windows, are windows made with two panes of glass separated by a layer of air or gas. The two panes of glass are typically separated by a spacer, which creates an insulating barrier between the two panes.

Cross Section Of A Double-Pane Or Double-Glazed Window
Source: Efficient Windows Collaborative

The space between the panes of glass can be filled with air or an inert gas, such as argon or krypton, which has better insulating properties than air. This insulating layer helps to reduce heat loss during the winter and heat gain during the summer, making double-pane windows more energy-efficient than single-pane windows.

For those who want to learn more, you can read more about how double-pane windows are manufactured at U.S. Window & Door’s comprehensive article on how single and double pane windows are made.

Double-pane windows can also reduce outside noise and increase security, as they are more difficult to break than single-pane windows. They are commonly used in residential and commercial buildings to improve energy efficiency and comfort.

Install Window Film on Double-Pane Windows: The Risks

So now that we know what double-pane windows are, why do people say window film shouldn’t be installed on it? The main reason is that window film will increase the temperature of the glass it is on which could cause thermal stress. Remember window film works by both reflecting AND absorbing heat,  so all window films will make the pane of glass it is installed on warmer because of absorption.

This only becomes a problem if the glass heats up too much. There are certain conditions that can cause this and the main one is if the glass absorbs too much heat. Let’s take a look at what thermal stress is and the causes:

Thermal Stress and Windows

Thermal stress is a physical phenomenon that occurs when an object is exposed to temperature changes. When an object is heated or cooled, its molecules expand or contract, causing the object to undergo thermal expansion or contraction. This can create stress within the object as different parts expand or contract at different rates.

Thermal stress can be problematic in materials such as glass, which have low coefficients of thermal expansion. This means that they expand or contract relatively little in response to changes in temperature. When such materials are exposed to rapid temperature changes or to extreme temperature differentials, they can experience significant stress, which can lead to cracking. The rapid warming can also cause a pressure differential inside the window that causes the seals to blow.

Thermal stress fractures in windows are rare and happen with or without film. The larger the pane of glass, the more likely it is to develop a blown seal or stress fracture. 

For example, during the night in some areas, temperatures may drop significantly and then when the sun rises, temperatures can rise quickly. The sunlight can cause the exterior surface of a window to become much warmer much faster than the interior surface. At night, the opposite may occur, with the exterior surface becoming much cooler than the interior surface.

If these temperature changes are significant enough, they can cause the glass to expand and contract, which can create thermal stress. Typically this will occur if there is a small chip or imperfection in the edge of the glass behind the frame.

Beyond heat absorption, there are some other contributing factors that can increase the risk of breakage that you should evaluate for.

Evaluate for other contributing factors

There are other factors that can contribute to thermal stress:

  • Windows that are already damaged, chipped, or cracked
  • Poorly designed or installed windows that do not allow for proper expansion and contraction of the glass
  • Direct exposure to hot or cold air currents, such as those created by heating or cooling systems
  • Shading of a portion of a window, but not all of the window
  • High altitudes (typically have greater temp swings from night to day)
  • Single glass panes larger than 40 square feet

Concord suggests that you evaluate your window conditions before purchasing any window film by using our handy guide to determine if your windows are a good fit for window film.

Again, it is important to keep in mind that the risk of this happening is very small.

Can you install window film on double-pane windows?

As we mentioned before, you can absolutely install window film on double-pane windows if:

Choose a film made for double-pane windows

First, it is important to select a window film that is suitable for use on double-pane windows. Some window films may not be compatible with double-pane windows, and it is important to check with the manufacturer to see if the film you are considering is suitable for double-pane windows.

In general, the industry standard is to NOT recommend window film that has an absorptance rate of greater than 50%. All window film works by reflecting AND absorbing solar energy so it doesn’t enter your home. If you want to install window film on double-pane windows and are worried about thermal stress, choose a film with as low an absorption rate as possible.

You can see in the performance specifications chart below that all ComforTech Ceramic Series films have a total solar absorptance of 50% or less and are appropriate for double-pane windows:

Comfortech Window Film Specifications Chart

All ComforTech™ Ceramic Series films are approved for use on double-pane glass less than 40 square feet in size.

To recap, films that cause excessive heat on a window that is in an area with large temperature swings, can lead to rupturing of the window seals (the units will fog up) or to glass breakage due to thermal stress. This situation is well known to the entire solar film industry. Films that absorb much of the solar energy rather than reflect it are more susceptible to causing this type of failure. Often these are the very light-colored films with minimal reflectivity. In general, films that have an absorption percentage of greater than 50% are typically not recommended for dual pane windows.

All Concord Window Films have an absorptance of 50 or less and are rated for double-pane window use. 

Install Window Film on Double Pane Windows Summary

The appropriate window film can be installed on double-pane windows that are in good condition and don’t have any contributing factors. If you live in an area of the country that doesn’t have fast temperature swings, this is less of an issue. If you have temperature swings, always check the manufacturer information to make sure you are purchasing a double-pane compatible film, and take a look at your window conditions using our guide linked above to see if any exist. When in doubt, choose a window film with a total solar absorbtance rate of 50 or less.

But, it is important to note that thermal shock and seal failure occur even on windows where no window film has been applied.  Less than 0.1% of all windows in the United States have window film applied to them, yet windows can and do break every single day.  This means that 99.9% of all windows that break don’t have window film as the cause. Essentially, installing film is increasing a very small risk, by a very small amount. And you can minimize the risk by choosing a film that is safe for double pane windows!

Also keep in mind that since their invention, double-pane windows have become the predominent window type used in U.S. homes over the past 20 years. So the majority of windows filmed in homes every year by all brands are double-pane windows. If it wasn’t safe to do, no one would be doing it.

Double-pane Safe Films at Concord Window Film

If you want to install window film on double-pane windows, you should know that every film we sell is double-pane safe on panes of glass that are less than 40 square feet in size! And the reality is that 90% of the film we sell gets installed on double-pane windows (the other 10% gets installed on single-pane or tempered windows) with no issues at all. It is definitely something to be cognizant of, but it shouldn’t prevent you from installing window film to upgrade your double-pane windows.

To learn more about ComforTech™ Ceramic Series window film for your double pane windows visit our website: www.windowfilm.com.

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