Polyester fiber), spandex (stretch nylon), nylon (nylon). Polyester characteristics: good air permeability, moisture desorption, and relatively strong resistance to acid and alkali and UV resistance. Advantages of spandex: high elasticity, high elasticity and good recovery. Weaknesses: Weak alkali resistance, easy to yellow and brittle after being exposed to chlorine or ultraviolet rays. Nylon advantages: high strength, high wear resistance, high chemical resistance, good resistance to deformation and aging. Disadvantages: It feels hard and is afraid of fire. Tutu sells backpacks of various materials.