High-reflectivity window films help block summer heat gain. They are best used in climates with long cooling seasons because they also block the sun’s heat in the winter.The effectiveness of these reflective films depends on many factors:
- Size of window glazing area
- Window orientation
- Building orientation
- Whether the window has interior insulation.
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 really benefit from them at all, and south-facing windows may benefit somewhat, but the benefit could be offset by the reduction of heat from the winter sun.
These films have some overall disadvantages:
- Loss of interior light or visible transmittance
- Impaired outside visibility
- Extra care required for cleaning
These reflective films are available to apply yourself over existing windows. Some window manufacturers also make reflective glazing or glass.