When sourcing Spunbond Polyester Mats, primarily used as a carrier base for bitumen membranes, you must prioritize Weight (GSM), typically ranging from 100g/m² to 250g/m². Key performance indicators include Tensile Strength (Longitudinal and Transverse) to ensure the mat doesn't tear during the bitumen coating process, and Elongation at Break, which should ideally be between 30% to 50% to accommodate structural shifts. Additionally, verify the Thermal Stability, as the mat must withstand temperatures of 180°C to 200°C during the saturation process without significant shrinkage.