Understanding Radiant Heat and Radiant Barriers
To best understand how radiant barriers work, it is essential to understand the principles of radiant heat. Radiant heat is the heat transferred between two objects that are not in direct contact. So, if one object was warmed by another object that it was not touching, the exchanged heat would be defined as radiant heat. Radiant heat is also defined as part of the light spectrum. As such travels at the speed of light and will continue travelling at that speed until absorbed or reflected. As can be guessed, Radiant Barriers and Reflective Insulation act as agents to reflect Radiant Heat.
For example, when placing your hand under a heat lamp the warmth can be felt emitting from the bulb. Should a Radiant Barrier or Reflective Insulation (reflective side facing the light emission) be placed in between the heating lamp and your hand it would be reflected. In effect, the Radiant Heat is no longer warming your hand because it is being reflected by the Radiant Barrier or Reflective Insulation.
Buildings act similarly to the hand in the above example where the heating lamp is the sun. Without a Radiant Barrier or Reflective Insulation the Radiant Heat a building will absorb radiant heat. And similar to the example above, if a Radiant Barrier or Reflective Insulation is place near the outer surface of the building it will effectively reflect Radiant Heat preventing the interior from absorbing Radiant Heat. It should be noted that the Radiant Barrier or Reflective Insulation will not just reflective the direct Radiant Heat observed in the visible light from the sun but also those sources of Radiant Heat that are reflecting and emitting absorbed Radiant Heat such as asphalt, mirrored buildings etc.