Desiccants refer to substances that can remove moisture from wet substances, and are often divided into two categories: chemical desiccants, such as calcium sulfate and calcium chloride, which are dried by combining with water to form hydrates; Physical desiccants, such as silica gel and activated alumina, are dried by physically adsorbing water.

The control of moisture is closely related to the yield of products. As far as food is concerned, under proper temperature and humidity, bacteria and molds in food will multiply at an alarming rate, which will make food rot and cause moisture and discoloration. Electronic products will also cause metal oxidation due to high humidity, resulting in defective products. The use of desiccant is to avoid the occurrence of defective products caused by excess water.

Desiccant, also called absorbent, is used to prevent moisture and mildew and plays a drying role. Desiccants for removing water vapor by adsorption include silica gel, alumina gel, molecular sieve, activated carbon, bone charcoal, charcoal, mineral desiccant, or activated clay. The commonly used adsorbents for removing water vapor by chemical absorption include calcium chloride, quicklime or phosphorus pentoxide, etc., which have great chemical affinity with water vapor. Absorbent is a kind of water-removing agent that absorbs moisture from the atmosphere. Its drying principle is to absorb water molecules in its own structure by physical means or to change its chemical structure by chemical means and become another substance.