Simply put, this is heat energy that is radiating through an air space. If a surface is hotter than the adjacent airspace, it will cast off its energy, in the form of heat rays, into that airspace. These rays are invisible, yet they are powerful.
Consider that temperatures in a dark attic can reach above 150 degrees, when the outside air is only 95 degrees. This is because the sun is saturating the roof with intense energy, which radiates into the attic below. This attic stays dark, but the energy released inside is intense.
Now consider what happens in a metal building. The roof absorbs the sun’s energy continuously throughout the day. Since energy cannot be created or destroyed, it can only be transferred or redirected. The metal casts this energy into the metal building in the form of invisible rays or energy. This energy manifests itself as heat when it strikes objects inside the building, including people. This, in turn, heats the surrounding air. The result is hot, stifling conditions inside the building.
The energy that is radiating into the building is mostly unaffected by mass insulation products. These materials absorb this energy, build heat themselves, and then cast this energy into the building. As the sun continues to provide energy, the interior of the building continues to receive it.
This energy can, however be controlled. Aluminum has the ability to redirect these invisible rays. This is why aluminum is used to insulate airplanes, the space shuttle, and even the spacesuits worn by astronauts. Without reflective materials, an astronaut would perish in space.
NASA even credits reflective insulation for allowing man and equipment to withstand the harsh environment of space orbit, where temperatures reach over 400 degrees in the sun, and less than minus 200 degrees in the dark.
When installed in metal buildings rFOIL effectively redirects the energy that radiates from the underside of the metal. A substantial portion of this energy is reflected upward, and not allowed inside the building.