Silica gel is frequently used as a desiccant for dehumidifying air or gas streams. Here, the water present in the air or gas is adsorbed by the silica gel. The adsorption capacity of the silica gel depends on its pore structure (see diagram). 

The diagram clearly shows that fine-pored A-type silica gels have their best water adsorption properties in the dry range of 0-60%  rel. humidity. Wide-porous B-type silica gels on the other hand are used in the range of 70-100% rel. humidity. If one requires the total spectrum, both types of silica gels can be mixed together.