Energy.gov on window film

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Government film recommendations

Window Films

Window films help block against solar heat gain and protect against glare and ultraviolet exposure. They are best used in climates with long cooling seasons, because they also block the sun's heat in the winter.

They can be useful for homeowners who don’t want to block views with other window treatments, but who have issues with glare and solar heat gain. They can also be a good choice on windows that are difficult to fit with other window treatments, or in places where artwork, furniture, or carpeting could be faded by UV exposure.

Films typically have three layers: an adhesive layer that sits against the glass, a polyester film layer, and a scratch-resistant coating. You may also choose options such as tints, UV blockers, or thicker films that offer security. Low-e films are also emerging as an energy-saving option.

Window films are the first window attachment to be rated by the National Fenestration Rating Council (NFRC), which also created window labeling and ratings for consumers. The NFRC’s Window Film Energy PerformanceNational Fenestration Rating Council (NFRC)

It includes the solar heat gain coefficient (SHGC) and visible transmittance (VT) of the window film, both numbers between 0 and 1. The lower the SHGC, the better the film is at blocking heat gain. The higher the VT, the more potential for daylighting. Read more about energy performance ratings.

The effectiveness of these reflective films depends on:

Silver, mirror-like films typically are more effective than the colored, more transparent ones. East- and west-facing windows, because of their greater potential for heat gain, can benefit more from these films. North-facing windows won't benefit from them, and south-facing windows may benefit somewhat, but the benefit could be offset by the reduction of heat from the winter sun.

Some window manufacturers also make reflective glazing or glass.