Silica gel is divided into: coarse-pore silica gel, B-type silica gel, fine-pore silica gel according to its pore size. Due to the different pore structures, their adsorption properties have their own characteristics. Coarse-pore silica gel has a higher adsorption capacity when the relative humidity is high, and fine-pore silica gel has a higher adsorption capacity than the coarse-pore silica gel when the relative humidity is low, while the B-type silica gel has a coarse and fine pore structure Between the pores, the amount of adsorption is also between the coarse and fine pores. Therefore, different varieties should be selected according to different uses.