When sourcing backpacks, the denier (D) count of the fabric is the primary indicator of durability. For heavy-duty or tactical use, prioritize 1000D Cordura or Ballistic Nylon. For everyday retail or promotional use, 600D Polyester offers a balance of cost and strength. Ensure the fabric has a PU (Polyurethane) or PVC coating on the reverse side to provide water resistance, and verify that the zippers are YKK or SBS brand to prevent mechanical failure, which is the most common cause of product returns.