What is the function of the shingle granule?
Granules serve a two-fold purpose. Primarily, granules block ultraviolet (UV) light from reaching the asphalt in the shingle. UV rays, if allowed to reach unprotected asphalt, will age the asphalt prematurely. Most manufacturers use only opaque granules across the entire surface of the shingle, including the top of the shingle; therefore the part of the shingle that is visible through the slot of a three-tab shingle should last just as long as the rest of the shingle.
