Buyers should prioritize Gram Weight (GSM), typically ranging from 100g/m² to 500g/m², as it directly impacts the material's tensile strength and durability. For compound fabrics, the bonding strength between the non-woven layer and the reinforcement (such as fiberglass or polyester mesh) is critical to prevent delamination. Additionally, verify the tensile strength (MD/CD) and elongation at break to ensure the fabric can withstand the mechanical stresses of bitumen saturation or coating processes.