All aluminum surfaces oxidize when exposed to oxygen. This chemical oxidation process forms a CLEAR natural layer over the surface. The thickness of this oxidation layer will increase until such a time that the layer becomes a solid protective layer that stops all further oxidation of the aluminum surface.
This oxidation process DOES NOT diminish the reflectivity of an aluminum radiant barrier because of the vast amount of aluminum remaining in the product under the clear oxidation layer.
However, this same oxidation process CAN AFFECT the reflectivity / emissivity of a metalized radiant barrier (which is merely a liquid aluminum sprayed onto a film or similar substrate), because there is very little aluminum remaining after the oxidation process has finally stopped. Therefore, for metallized radiant barriers to maintain their reflectivity, they MUST BE COATED with a protective coating to guard against oxidation.
Our RadiantGUARD® XTREME radiant barrier has been coated with a proprietary surface coating to protect against oxidation and passes the ASTM D3310 Corrosivity test.