The natural light and airflow large windows provide are great for your well-being, but all that glass also makes it harder to control your indoor temperatures. While curtains and other window treatments help, they tend to get in the way. With window insulation film, you can control the warmth and light entering your home without obscuring the view. Window film offers measurable benefits, but these films work better in some situations than others.
An Easy Upgrade for Comfort
Window insulation film is a thin layer of plastic, usually polyethylene teraphthalate (PET), applied to a window to control heat transfer and light. It’s used to keep homes cooler in the summer and protect carpets and furniture from fading caused by ultraviolet light exposure, as well as to hold in heat during winter. Relatively cheap and easy to install, window film is a practical way to improve the performance of your old windows until you can upgrade to more energy-efficient windows.
You’ll find two main types of window film on the market:
Solar control film – This film reduces solar radiation by reflecting the sun’s infra-red rays and absorbing its UV rays. Designed to last a decade or longer, it’s applied directly to the window glass.
Convection control film – This film works like double glazing to reduce heat conduction, creating a gap that slows the transfer of heat from the window to the air. It’s installed on the window frame and most often used in cold climates during winter, then removed in spring.
Getting the Most from Your Window Film
Whether or not window films are worth it for you depends on several factors, including your climate, budget, existing windows, and goals.
If your main objective is to keep your home cooler in summer and reduce your air conditioning bills, solar film is a good bet. Modern solar films can block as much as 55 percent of the outdoor heat. In a warm climate such as California, it can reduce your cooling costs by as much as 30 percent. These films also block 99 percent of the UV light that fades furniture while only minimally reducing visible light.
In cold climates, a solar window film applied directly to the window absorbs the sun’s warmth and re-radiates heat into your home’s interior. An insulating window film applied over a window can help the window retain up to 55 percent more heat in winter, potentially reducing your heating costs up to 30 percent. These films are less effective at reducing summer heat gain, though.
While that’s definitely a plus, it’s still not the same benefit you’d get from a double-pane window. A layer of plastic just isn’t thick enough to slow heat transfer the way a second pane of glass would.
Climate control window films run between $7 to $15 per square foot. DIY window insulation film kits are available for between $10 and $30, letting you insulate your windows for as little as $3 per window.
That’s much cheaper than double-pane, low-e windows, which cost between $30 and $55 per square foot. The price difference means window film is typically used as a budget-friendly retrofit to boost the energy efficiency of windows that are old, but still in good condition. On the other hand, professionally installed high-quality solar films can help a cheaper new window reach the same efficiency as a pricy low-E, triple-pane window.
Research Before You Buy
Before you settle on installing window film, check the warranty on your windows. Most DIY insulation films are easy to remove and won’t affect the window’s warranty. Solar films applied to the glass, however, can void some manufacturers’ warranties. On the other hand, some window film manufacturers are willing to match the window’s warranty.
If you opt for solar film, use the film’s light-to-solar gain (LSG) ratio to get the right type for your climate. LSG is the ratio of the film’s solar heat gain coefficient (SHGC) to its visible transmittance (VT). If you’re trying to stay cool in a warm climate, choose a film with an LSG over 1, meaning a VT value higher than its SHGC value. If you’re in a cold climate and want to hold on to your heat, choose a film with an LSG of less than 1.
Not all films are as effective or durable as their manufacturers claim, so do your homework before you buy. Local glaziers and window film installers can offer recommendations, but it’s still wise to read each product’s specifications and reviews. For solar film, look for National Fenestration Rating Council (NFRC) certification.
The effectiveness of any window film depends on correct installation. For solar film, hire a professional who can apply the film without unsightly ripples and bubbles, or gaps that reduce the film’s efficiency and lifespan.
For a DIY insulation film kit, start by cleaning the window and frame to remove dust that could prevent the tape from adhering. Measure and cut the film carefully to avoid creating gaps. Apply the tape to the window frame, then attach the film starting from an upper corner. To finish, run a hair dryer on a high setting around the window frame to shrink the plastic and seal the edges. This final step isn’t essential for effective insulation, but it will give you a clearer, more attractive finish.
While most window insulation films can’t provide the same benefits as new low-E, double-pane windows, they can keep you a little more comfortable. Even a basic insulation film kit will do a lot if you live in a cold climate and have single-pane windows. If you’re in a hot climate, professionally installed solar film is an affordable way to protect your interior from the sun.