When the goal is having a cooler home, we need to examine the surface temperatures in the attic. Remember, the attic has both surface temperatures and air temperatures.
Bottom line: getting a cooler, more efficient home is all about the surface temperatures.
Surface temps can only be measured with an infrared thermometer, while air temps can be measured with probe thermometers. The surface temperatures in your attic are basically what tell your home whether or not it is hot outside; this directly effects whether or not your air conditioner turns on and runs. When the attic gains radiant heat from outside, it re-radiates that heat through the attic air and the insulation on your attic floor absorbs it. When your insulation is 130 degrees, your house thinks it’s 130 degrees outside because it essentially has a 130 degree blanket on top of it! By stopping the radiant heat gain in the insulation, with a layer of radiant barrier foil, we can reduce the top surface temperature of the insulation and when the insulation is cooler, the home is cooler and the air conditioner is more efficient.