When sourcing micro polyester staple fiber (typically defined as less than 1.0 denier), you must prioritize denier accuracy (e.g., 0.7D, 0.8D, or 0.9D), as this directly impacts the softness and 'down-like' feel of the end product. Additionally, check the cut length (commonly 32mm or 51mm) to ensure compatibility with your spinning or non-woven production machinery. Other critical metrics include tenacity (strength), elongation at break, and the oil pick-up (OPU) percentage, which affects the fiber's processability and static generation during manufacturing.