As the sun beats down on the roof of a home, its radiant energy make the surface of the roof hot. Through conduction, the underlying roof materials get hot too. The heat is then radiated onto cooler surfaces in the attic, where it can then be transferred into the home itself. This heat counteracts the cooling that’s being accomplished by the air conditioning system, forcing it to work harder. Also, this can make it much more difficult to achieve optimal indoor comfort on especially hot days.
How Metal Roofing and Radiant Barriers Help
Metal Roofs reflect heat - unlike other roofing materials that absorb heat.  The problem with a metal roof is that it reflects the heat in both directions.  That problem is solved by installing a radiant barrier below the metal roofing material.  Radiant barriers use highly reflective materials, most typically aluminum to deflect radiation from the sun. In turn, the radiant heat can’t warm up the attic.
They just need to be perpendicular to the source of radiant energy and must face open air space.  The open air space is created by the use of the CDR (Complete Drained Roof Vent) which is installed between the metal roofing and the radiant barrier, this reflects up to 97% of the heat and is allowed to vent at the peak of the roof by installing custom roof vents.