When evaluating Spun Polyester, you must focus on the Yarn Count (e.g., 20s, 30s, 40s) which determines the thickness and weight of the final product. For sewing threads, look for high tensile strength and low shrinkage rates (typically <2%) to ensure durability during high-speed stitching. If purchasing fabric, verify the GSM (Grams per Square Meter) to match your specific application, whether it be for lightweight apparel or heavy-duty upholstery. Additionally, ensure the material has undergone anti-pilling treatment, as spun fibers are more prone to pilling than filaments.