When sourcing plastic threads (such as polyester, nylon, or polypropylene), the price is primarily driven by material purity, denier (thickness), and tensile strength. You should prioritize suppliers who provide technical data sheets (TDS). High-quality threads must have high tenacity (measured in g/d) and low shrinkage rates to ensure durability during high-speed sewing or weaving. Always verify if the price includes UV stabilization or flame-retardant treatments, as these additives significantly impact the final cost but are essential for outdoor or safety-critical applications.