Like most products that perform one or more technical functions, window film carries with it a set of terms that may be over the head of the average consumer at first glance. There certainly are words we’ve all seen and used – light energy, heat energy, even ultraviolet and infrared. Beyond those, there are the more scientific terms, like reflectance, transmittance, and absorption.

Window film language gets even more technical than that. Is it important for you to know and grasp every window film technical term? Of course not. But familiarity with some of the basic language used to describe how window film works will help you make a more informed purchasing decision. You’ll better understand the differing functions of various films, which allows you to make a smart choice. And you’ll level the playing field a bit when it comes to talking with the window film professional who estimates and installs your project.

Here is a bit of window film terminology to know:

Total Solar Energy

This is the entire spectrum of the sun’s energy that reaches the earth’s surface. It’s made up of visible light, ultraviolet (UV) light, both UVA and UVB, and infrared (IR) energy. Window films manage all of these types of energy to some degree, and for different purposes.

Visible Light Transmitted

This is a measurement of the amount of sunlight a piece of glass lets through. A very dark window film may transmit only 5-10% of visible light into a room, while a light or nearly clear film may allow 90% and up. Visible Light Reflected indicates how much light is bounced back to the source, whether the source is the sun outside or the building’s interior lighting.

UV Rejection

Damage is caused to interior furnishings and carpet, not to mention to the skin of room occupants, by UV rays. UV rejection tells you how much of this harmful radiation is turned away by the window film.


Emissivity is essentially the insulating quality of a piece of glass or of the window film covering it. Low-emissivity (Low-E) films reflect a great deal of the heat generated on a building’s interior back inside, a desirable quality for window films installed in colder climates.


U-Factor indicates the level of heat energy, independent of the sun’s radiant energy, that passes through a glass/window film assembly. It’s calculated with a multiple of the difference between indoor and outdoor air temperatures, and like Low-E, a lower U-Factor number means better heat retention inside a building in cold weather.

Talking the window film talk will give you an advantage when it comes to selecting a window film product and getting the greatest value from your purchase. For the exceptionally scientific-minded, a full glossary of window film terminology provides an even deeper look into the functionality of these products.

Download Glossary of Terms