⚡ QUICK ANSWER
A container desiccant is a moisture-absorbing product placed inside a shipping container to remove water vapour from the air and prevent condensation (“container rain” or “cargo sweat”) from damaging goods. Most container desiccants use calcium chloride because it absorbs many times its own weight in moisture and keeps working across long ocean voyages, protecting cargo from mould, rust, caking and corrosion.
📊 KEY FIGURES
• Container desiccants target the water vapour that causes container rain — a top cause of moisture-related cargo claims.
• Calcium chloride desiccants absorb up to ~200–300% of their own weight.
• A 40ft container encloses roughly 67 m³ of air that cycles through daily temperature swings.
• Common damaged goods without protection: textiles, food, coffee, leather, electronics, machinery.
What is a container desiccant?
A container desiccant is a desiccant (moisture absorber) specifically designed to protect goods inside a shipping container. It is placed in the container before the doors close and works throughout transit, pulling water vapour out of the air so it cannot condense onto the cargo.
The word “desiccant” simply means a substance that removes moisture. What makes a container desiccant different from a small sachet in a shoebox is scale: it has to keep a large, sealed, temperature-cycling space dry for weeks, not keep one small package dry for a few days.
Why is moisture a problem inside shipping containers?
A shipping container is a sealed steel box. During the day it heats up and the air inside holds more water vapour; at night the steel cools and that vapour condenses into droplets on the ceiling and walls. Those droplets fall onto the cargo — a phenomenon called container rain or cargo sweat.
Repeated over a multi-week voyage, this causes real damage:
- Mould and mildew on textiles, leather and paper.
- Rust and corrosion on metal parts and machinery.
- Caking and clumping of powders, food and agricultural goods.
- Label lift, packaging failure and water staining.
How does a container desiccant work?
Container desiccants remove moisture in one of two ways. Adsorbents like silica gel hold water on the surface of their pores. Absorbents like calcium chloride chemically bind water and convert it into a stable gel that cannot be released back into the container.
Calcium chloride is the most common choice for containers because of its very high capacity and because it locks moisture away permanently — even when temperatures rise again later in the voyage.
What types of container desiccant are there?
| Type | Capacity | Typical use |
|---|---|---|
| Calcium chloride | Very high | Full containers, long / humid voyages |
| Silica gel | Low | Small sealed packs inside the container |
| Clay / bentonite | Low | Low-cost, short, dry routes |
| Molecular sieve | Moderate–high | Very low target humidity |
Calcium chloride desiccants also come in different formats — pole, hanging strip, blanket and in-box — so they can be matched to how the cargo is stowed.
How do you choose and use a container desiccant?
Choosing the right container desiccant comes down to a few decisions, each covered in more detail in our related guides:
- Material — calcium chloride for containers; silica gel only for small sealed packs.
- Format — pole, hanging or blanket to match your stow.
- Quantity — based on container size, voyage length and cargo moisture.
- Supplier — verified capacity, leak-resistant construction and relevant certifications.
Place absorbers where condensation forms first — high on the walls and in pallet voids — and choose fresh desiccant for every shipment.
Frequently Asked Questions
What is a container desiccant used for?
It is used to absorb water vapour inside a shipping container so that condensation (container rain / cargo sweat) does not form and damage the goods. It protects cargo such as textiles, food, leather, electronics and machinery from mould, rust and caking during transit.
What is the best desiccant for a shipping container?
A container-grade calcium chloride desiccant, because it absorbs many times its own weight in moisture and keeps working through the temperature swings of an ocean voyage — far more than silica gel or clay.
How is a container desiccant different from a silica gel packet?
Scale and chemistry. A silica gel packet keeps one small package dry for a short time by holding water on its surface. A container desiccant — usually calcium chloride — keeps a whole container dry for weeks by chemically absorbing and locking away far more moisture.
How many container desiccants do I need?
It depends on container size, voyage length and cargo. As a rough planning start, about 1–1.5 kg of calcium chloride per 20ft of space in normal conditions, more for humid or long trips. Confirm the exact quantity with your supplier.