Softening resin is a specialized resin used for softening hard water, which uses ion exchange technology to make the hardness of water less than 50 mg/L (CaCO3). Ion exchange is a special dynamic adsorption process, usually carried out by insoluble ion exchangers in electrolyte solutions, which are ion exchange resins.

More than half of ion exchange devices are used for water treatment desalination, and the main types of water treatment desalination are strong acidic hydrogen cation exchange resins and strong alkaline hydroxide anion exchange resins. When hydrogen cation exchange resin comes into contact with water, an ion exchange reaction occurs, and various cations in water are adsorbed on the resin, while the hydrogen ions bound to the cation resin are exchanged. At this time, the water only contains one cation, hydrogen ions. When the hydroxide anion resin comes into contact with water and undergoes an ion exchange reaction, various anions in the water are adsorbed, resulting in only one hydroxide ion in the water. When the water passes through this hydroxide cation resin and then through the hydroxide anion resin, only two types of cations and anions (hydrogen ions and hydroxide ions) will combine to form water, completing the desalination process of water.