Several factors influence the performance of GAF modified bitumen cap sheets in asphalt or bitumen modification systems. Key factors include the type and percentage of polymer used for modification, the compatibility of the modifier with the base bitumen, the application temperature, and the thickness of the cap sheet. Additionally, environmental conditions such as UV exposure, temperature fluctuations, and moisture can significantly impact the durability and adhesion properties of the modified bitumen. Proper installation techniques also play a crucial role in performance.