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:
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.
See our complete line of Dual Reflective Window Films which have a highly reflective outside layer for high solar heat rejection with a lower reflective shaded layer for your inside view.