Without a radiant heat barrier:

The sun radiates heat to the roof, the roof deck, the attic insulation, and to anyone inside the home.

With a radiant heat barrier:

97% of the heat is reflected off the metal roof radiant barrier, preventing heat from radiating into the home

Solar Radiant Heat – How It Works

P.O. Box 337, Brattleboro, VT 05302 - 877.999.5539