The Complete Handbook of Window Films

Chapter 1: Understanding Window Films

Before you read a single spec sheet, you should understand what you are actually looking at: a window film is a thin, multi-layered polyester membrane, typically 0.001 to 0.014 inches thick, that is adhered to a pane of glass. It is not a coating that is painted on, and it is not a replacement for the glass itself. It is an aftermarket product that modifies the behavior of already-installed windows by filtering sunlight and adding either structural reinforcement or optical effects. Most films are installed on the interior side of the glass, but there are exterior films for specific conditions, and there are automotive films with their own separate standards.

To understand how film works, you need to know what happens to sunlight when it hits an uncoated pane of glass. The glass reflects some of the light and heat off its surface. It absorbs a small amount of the energy and becomes slightly warm. The rest passes straight through into the building, carrying visible light, ultraviolet radiation, and infrared heat into the interior. This is not abstract physics that you can safely ignore. The ultraviolet component is what fades upholstery and hardwoods, the infrared component is what makes a west-facing living room feel like an oven on a summer afternoon, and the visible component is what causes glare on televisions and computer screens. Thirty percent of a typical building's cooling load comes from solar heat gain through glazing. Even on a cold, sunny winter