GAF shingles are at the leading edge of the industry in quality and longevity. There are three important features that only GAF provides in their product. First, the shingle matting is woven in four directions, which provides for the most solid structural integrity. Second, the shingles contain no chemical or organic fillers, which provide for increased thickness and weight but decreases the resilience and longevity of the shingles. Third, GAF uses an optimal ratio (65/35) of pure limestone to ensure that the asphalt will maintain its strength through time. Too little limestone and the shingles become soft, too much and the shingles will become too brittle. Together, these features create a durable shingle that will stand the test of time.