Selecting the correct thread depends on the balance between tensile strength and elasticity. For heavy-duty items like leather goods, automotive upholstery, or outdoor gear, Nylon 6.6 (Bonded Nylon) is the industry standard due to its high heat resistance and anti-fray properties. For apparel or lightweight textiles, Nylon 6 offers better cost-efficiency and flexibility. Always verify the denier or tex size (e.g., T70 for general upholstery, T210 for heavy luggage) to ensure compatibility with your machinery's needle size.