The choice depends on the kite type and skill level. Cotton thread is suitable for small, lightweight kites but lacks durability. Nylon thread offers high elasticity and strength, making it ideal for beginner single-line kites. Polyester (Dacron) is the industry standard for most B2B buyers due to its low stretch, high UV resistance, and excellent knot strength. For professional stunt or power kites, Spectra or Dyneema fibers are preferred because they are ultra-thin, have near-zero stretch, and provide maximum tensile strength.