FREE SHIPPING ON PRECUT KIT ORDERS OF $100 OR MORE
Menu
Not a frequently asked question, but something that does come up every so often is why is my glass hotter with window film?
If you’ve installed window film expecting a cooler interior and better energy efficiency, you might be puzzled to find that the glass itself feels hotter to the touch. This can seem counterintuitive, especially if your goal is to reduce heat.
In this blog, we’ll dive into why the glass might feel hotter with window film and explain how this doesn’t mean your window film isn’t working—in fact, it’s a sign that it is!
Window film, particularly solar control window film, is designed to block a significant portion of solar heat before it can enter your home. It does this two ways: by reflecting or absorbing solar energy, which is responsible for the heat buildup inside your home.
High-performance films, such as ceramic window films, reflect a significant portion of the sun’s rays, redirecting heat before it can pass through the glass.
Less reflective films (often lighter films) control solar energy by absorbing more of it than reflecting it. The solar heat is then dissipated, preventing it from entering your living space.
Both of these processes reduce the amount of heat entering your home, but as the film works to reflect or absorb solar energy, it will naturally transfer some of that heat to the glass making the glass hotter.
The performance specifications that we provide show the amount of solar energy that each shade of our ceramic film reflects and absorbs.
You can see that the darker the film, the more reflective it is (Total Solar Reflectance) and the less solar energy it absorbs (Total Solar Absorbtance).
The glass is hotter because when window film is applied, more of the sun’s energy stays in the glass. This is because, without film, much of the solar energy passes through the glass and into your home.
With window film, the energy is either reflected or absorbed by the glass and the film. The result is that the glass can feel warmer to the touch.
No. The glass feeling hotter does not mean your window film isn’t performing its intended function. Quite the opposite—it’s a sign that your film is successfully preventing heat from entering your home.
It is important to note that our film is rated according to the National Fenestration Rating Council’s standards for window film. The two key measurements that the NFRC uses to rate the solar control of any window film are: Total Solar Energy Rejected and Solar Heat Gain Coefficient.
Total solar energy rejected is a measure of how much solar energy the filmed glass will reject or prevent from getting into the home. The higher the number, the more solar control the filmed glass provides.
The solar heat gain coefficient is a measure of how much heat the filmed glass lets into a building. This measurement takes into account the amount of direct heat that makes it through AND the amount of incidental heat that enters due to convection from the absorbed heat. The lower the SHGC, the less heat is entering the home.
You can see from our window film performance specifications, that all our ComforTech™ Ceramic Series film shades reduce the amount of heat that enters the home.
Instead of focusing on the temperature of the window glass, a better way to measure the efficacy of the film is to measure the temperature of the room before and after film. Another way is to take a measurement of the floor or a piece of furniture a few feet into the room before and after film is installed.
The heat you feel on your window glass is not a sign of a problem, but rather a confirmation that your window film is working to block heat from entering your home. By absorbing or reflecting solar energy, the film keeps your home cooler and more comfortable, all while reducing your energy costs.
If you’re considering installing window film or looking to upgrade, explore our range of solar control window films to find the right product for your needs. You’ll enjoy the benefits of a cooler interior, UV protection, and energy savings—all without compromising the natural light you love.
