Desiccant & silica gel glossary

New to desiccants? This glossary explains the terms manufacturers, buyers and quality teams use when specifying moisture-control products. Where relevant, each entry links to the product or guide that covers it in depth.

Adsorption

The process by which molecules of water vapour (or gases) adhere to the surface of a material. Silica gel, molecular sieve and activated carbon are all adsorbents — they trap moisture on their vast internal surface area rather than chemically reacting with it.

Absorption

A process in which one substance is taken up into the bulk of another, unlike surface-only adsorption. Some desiccants such as calcium chloride absorb moisture and deliquesce (turn to liquid), whereas silica gel adsorbs while staying dry to the touch.

Desiccant

A material used to remove moisture and maintain a dry environment inside packaging or equipment. Common desiccants include silica gel, clay, molecular sieve and activated carbon.

See our desiccants

Silica Gel

A synthetic, highly porous form of silicon dioxide and the most widely used desiccant. It can adsorb up to about 40% of its weight in moisture and is non-toxic, chemically inert and reusable.

Silica Gel Bag

Indicating Silica Gel

Silica gel treated with a dye that changes colour as it saturates, giving a visual indication of remaining capacity. Blue indicating gel turns from blue to pink; cobalt-free orange gel turns from orange to green.

Silica Gel Blue

Non-indicating Silica Gel

White silica gel with no colour-change dye. Because it is cobalt-free it is the preferred choice for food and pharmaceutical packaging.

Silica Gel White

Cobalt Chloride

The moisture indicator used in traditional blue silica gel. It causes the blue-to-pink colour change but is restricted near food and pharmaceuticals, which is why cobalt-free orange gel is used in those sectors.

Silica Gel Orange

Molecular Sieve

A synthetic zeolite with a uniform, precisely-sized pore structure that adsorbs water and other molecules by size and polarity. It dries to extremely low moisture levels and holds moisture even at low humidity.

Molecular Sieve

Zeolite

A crystalline aluminosilicate mineral, natural or synthetic, with a regular microporous structure. Molecular sieves are manufactured zeolites used for precision drying and gas separation.

Activated Carbon

A highly porous carbon adsorbent that captures odours, gases and volatile organic compounds (VOCs) in addition to some moisture — ideal where both humidity and smell must be controlled.

Activated Carbon

Clay Desiccant

A natural desiccant made from activated montmorillonite clay. It absorbs 25–30% of its weight in moisture and is an economical choice for high-volume packaging and container shipping.

Clay Desiccant

Montmorillonite

The natural clay mineral from which clay desiccant is produced. It adsorbs moisture physically without any chemical reaction, and is non-toxic and biodegradable.

Relative Humidity (RH)

The amount of water vapour in the air expressed as a percentage of the maximum the air can hold at that temperature. Controlling RH inside packaging is the core job of a desiccant.

Dew Point

The temperature at which air becomes saturated and water begins to condense. Lowering the dew point inside sealed packaging or systems prevents condensation and corrosion.

Equilibrium Relative Humidity (ERH)

The humidity level at which a product neither gains nor loses moisture. Desiccants are sized to keep packaging below a product's critical ERH so it stays stable.

Moisture Absorption Capacity

The maximum weight of moisture a desiccant can hold, expressed as a percentage of its own weight. Silica gel reaches up to ~40%, clay 25–30% and molecular sieve ~22% (but at much lower humidity).

Regeneration (Reactivation)

Restoring a saturated desiccant by heating it to drive off adsorbed moisture. Silica gel is typically reactivated at 110–120°C, then cooled in a sealed container before reuse.

How to store desiccants

Mesh Size

The particle-size grading of silica gel beads or crystals (e.g. 3–8 mesh, 9–16 mesh). Larger beads adsorb more slowly but resist dusting; finer grades act faster.

Container Rain

Condensation that forms on the inside of a shipping container when humid air cools overnight and drips onto cargo. Container desiccants prevent it by adsorbing the excess moisture.

Packaging & logistics

Humidity Indicator Card (HIC)

A card printed with moisture-sensitive spots that change colour at set RH levels, placed inside packaging to verify that the desiccant is keeping humidity in range.

Non-woven Fabric

The breathable, dust-free material used to make silica gel sachets. It allows water vapour through to the gel while containing the beads, and carries the standard 'do not eat' warning.

Transformer Breather

A device on electrical transformers filled with indicating silica gel that dries the air drawn into the oil conservator, protecting insulation from moisture.

Power & instrumentation

Bead vs Crystal

Two physical forms of silica gel. Beads are smooth, near-spherical and low-dusting; crystals (granules) are irregular. Both adsorb moisture equally; the choice is about dusting and appearance.

VOC (Volatile Organic Compound)

Organic chemicals that readily evaporate and can cause odours or contamination. Activated carbon is used to adsorb VOCs alongside moisture control.