When evaluating Flyknit shoes, the upper material composition is paramount; look for high-tenacity polyester yarns or recycled PET fibers to ensure a balance of breathability and durability. The knitting density (gauge) should be varied across the foot—tightly knit in the heel for support and more open in the forefoot for ventilation. Additionally, verify the outsole material, typically TPU or Phylon, and ensure the bonding strength between the knit upper and the sole meets the ISO 20875 standard to prevent delamination.