The moisture absorption and air permeability are observed under a 2000x electron microscope. The cross section of bamboo fiber is concave and convex, filled with nearly elliptical pores, and is highly hollow. The capillary effect is extremely strong. It can absorb and evaporate water instantly. Among all natural fibers, bamboo fiber has the best moisture absorption, desorption and air permeability among the five major fibers, and its far-infrared emissivity is up to 0.87, which is much better than traditional fiber fabrics. Therefore, it meets the characteristics of thermal comfort. At 36 ° C; When the relative humidity is 100%, the moisture regain of bamboo fiber is more than 45%, and the air permeability is 3.5 times stronger than that of cotton. It is reputed as the "breathable fiber" and also called the "fiber queen".