A hygroscopic substance is one that readily attracts water from its surroundings, through either absorption or adsorption.
Most hygroscopic materials are salts, but many other materials display the property.
Examples of Hygroscopic Materials
- Zinc chloride, sodium chloride, and sodium hydroxide crystals are hygroscopic, as are silica gel, honey, nylon, and ethanol.
- Sulfuric acid is hygroscopic, not only when concentrated but also when reduced down to a concentration of 10% v/v or even lower.
- Germinating seeds are hygroscopic. After seeds have dried, their outer coating becomes hygroscopic and begins absorbing the moisture required for germination. Some seeds have hygroscopic portions that cause the shape of the seed to change when moisture is absorbed. The seed of Hesperostipa comatatwists and untwists, depending on its hydration level, drilling the seed into the soil.