Asphalt shingles can collect and absorb moisture. Because of this, algae can form on the surface of the shingle. Certainteed coats there shingle granules with a layer of copper and a ceramic coating, giving the shingle a layer of protection that prevents algae from forming. This way we can keep you roof from getting that nasty looking black streaking that can be an eye sore. We carry a 10 year StreakFighter Warranty to back that claim up!