Also known as: Silica Gel, Moisture Absorber, Drying Agent
A desiccant absorbs water vapour from the air inside a sealed pack, lowering humidity so condensation and corrosion cannot occur. Silica gel and clay are the common types, dosed by pack volume rather than guesswork.
Sealed containers experience daily temperature swings, and each swing can drive humid air past the dew point. That condensation is what rusts parts and softens cartons on a long sea voyage — the phenomenon shippers call container rain.
A desiccant absorbs the moisture before it can condense. Silica gel is the standard for general use; clay is cheaper and works well at ambient temperature; molecular sieve is used where very low humidity is required.
Dosing matters and is routinely got wrong. Requirement is calculated from the enclosed volume, the moisture already present in the packaging materials and the expected transit duration — a single sachet in a container does nothing at all.
For metal parts, desiccants are frequently paired with VCI. The desiccant reduces the moisture load while the VCI protects the surface directly, which is more reliable than either on its own.
Desiccant at a glance
| Common types | Silica gel, activated clay, molecular sieve |
|---|---|
| Measurement unit | DU (desiccant unit) |
| Capacity | Silica gel absorbs roughly 20–35% of its weight |
| Dosing basis | Enclosed volume, material moisture, transit time |
| Requirement | Needs a genuinely sealed enclosure to work |
| Often paired with | VCI for metal parts |
Common questions
How much desiccant do I need for a shipping container?
It is calculated from enclosed volume, the moisture held in the packaging and pallets, and transit duration — commonly several kilograms for a full container. A few sachets achieve nothing at that scale.
Can I use a desiccant instead of VCI for metal parts?
Only for mild cases. A desiccant lowers humidity but does not protect the metal surface itself or reach into bores and threads. For valuable machined parts, use both.
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