What is the most important performance characteristic for granules on asphalt shingles?

The most important performance characteristic for granules on asphalt shingles is their role in protecting the coating grade asphalt surface. The granules serve a crucial function by acting as a barrier against ultraviolet (UV) rays from the sun, which can degrade the asphalt over time. This protection helps to prolong the lifespan of the shingles and maintain their integrity against environmental elements.

Moreover, granules provide a level of fire resistance and improve the overall durability of the roofing material, as they shield the underlying asphalt from moisture and other damaging factors. While enhancing color and providing insulation may have their own benefits, they do not reflect the primary functional purpose that ensures the long-term performance of asphalt shingles. Similarly, increasing the weight of the shingle is generally not a desired feature; it's the protective role that is paramount for maintaining the shingle's effectiveness.