Desiccant

A material that lowers humidity by taking up water vapor through absorption or adsorption. Desiccants are used to keep enclosed spaces and products dry.

Adsorption: The accumulation of molecules at the surface of a solid or liquid. Silica gel captures water vapor mainly on its internal surfaces.
Relative humidity: The ratio of water vapor present in air to the maximum amount possible at the same temperature, expressed as a percentage. It describes the atmospheric moisture desiccants are used to reduce.
Silica gel: A porous, amorphous form of silicon dioxide used to adsorb moisture. It is a familiar reusable desiccant in packets and storage containers.
Dehumidifier: A device that removes water from air by condensation, adsorption, or another moisture-control process. Unlike a desiccant packet, it actively treats air in a room or system.
Absorption: The uptake of one substance into the bulk of another. Some desiccants take water into their bulk rather than only onto a surface.
Water vapor: Water in its gaseous state, present in the atmosphere and other environments. This is the moisture desiccants capture from their surroundings.
Molecular sieve: A porous material with uniform pores that selectively adsorbs molecules according to size and affinity. It dries gases and liquids when very low moisture levels are needed.
Humidifier: A device that adds water vapor or droplets to indoor air. It raises humidity, the opposite of the usual aim of a desiccant.
Deliquescence: The process by which a solid absorbs enough atmospheric moisture to dissolve into a liquid solution. Calcium chloride desiccant can deliquesce as it draws water from air.
Porous material: A solid containing pores or voids that can hold gases or liquids. Many desiccants use internal pore area to capture large amounts of vapor.

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