Reflective film is typically made out of one or more layers of polyester, and is often applied to windows in commercial and residential settings. This film is used mainly to improve energy efficiency by lowering the amount of heat entering a building as a result of sunlight. Other benefits can include increasing privacy and shatter resistance, as well as reducing the amount of ultraviolet (UV) light that can damage furnishings and fabrics. Installation is a relatively simple process and can usually be done either professionally or as a home improvement project.
Most of these films consist of layers of polyester that have had dyes or metallic elements added to darken the film and increase light reflectivity. Dyes darken the film, but reduce clarity. Metal coatings increase light reflection, but can lead to more reflectivity than is desired. Both dyes and metal additives have benefits and drawbacks, which is why reflective films often contain a combination of both, to maximize the benefits of each type of additive.
One of the most common reasons for installing reflective film on windows is to increase energy efficiency. Reflective film basically works by reflecting much of the heat from sunlight, causing the heat to be stored in the window glass while preventing some of the heat from entering the building. The heat in the glass is moved away by the wind, which is typically much stronger outdoors than indoors. Heating and cooling costs can be significantly decreased with installation of reflective film. Additional benefits may include increased privacy, reduced glare and UV light, and improved shatter-resistance.
Many types of consumer grade reflective films have adhesive on one side and are applied directly to the window that faces the interior of the building. These varieties are usually designed for use on single-thickness glass and are not normally recommended for use on double-glazed windows, plastic, damaged glass, or glass over 40 years old. Installation is considered to be relatively easy, and can often be done by the homeowner. The film tends to wrinkle easily, and these creases cannot be removed. It may be a good idea to have two people install the film on large windows to avoid this problem.
Reflective film offers a number of benefits, but there are a few potential drawbacks to consider before purchasing it. Dyed or tinted window films may significantly reduce the amount of natural, visible light allowed into a space. This can result in a need for more interior lighting, which may lead to higher energy use. Highly reflective films can have a mirrored appearance that may be less attractive and may also prove to be a glare nuisance to neighbors.