Calcium Chloride Container Desiccant: Specs, Capacity & Dosage

When importers ask us which desiccant to hang in a container, the answer is almost always the same: calcium chloride. It is the workhorse of ocean-freight moisture protection, and for Gulf-bound cargo in particular it outperforms every alternative in the conditions that actually cause damage. This guide explains how it works, how it is specified, and how to use it correctly.

What Calcium Chloride Desiccant Is

Calcium chloride (CaCl₂) is a highly hygroscopic salt — it attracts and holds water vapour from the air. In a container desiccant it is packed in a breathable sachet or bag with an absorbent inner layer. As it absorbs moisture, the salt dissolves into a brine that stays locked inside the bag, so water never leaks onto the cargo.

A well-designed calcium chloride container desiccant can absorb 100–200% of its own weight in water vapour over a long voyage. A 1 kg unit, in other words, may take up 1–2 litres of water before it is spent — several times more than an equal weight of silica gel under the same humid conditions.

Why It Beats Other Desiccants for Container Shipping

The key advantage is performance at high relative humidity. In a container crossing the tropics or sitting on a Gulf quay, relative humidity can exceed 80–90%. Silica gel loses efficiency as RH climbs, while calcium chloride keeps absorbing — which is exactly when you need it most.

How to Specify the Quantity

As a working baseline for a 20–30 day voyage:

• 20ft container: 6–10 units of 1 kg for general cargo; 10–16 for damp or hygroscopic cargo.
• 40ft container: 12–20 units for general cargo; 20–32 for hygroscopic cargo.
• 40ft High Cube: scale up roughly 10–15% for the extra volume.

Increase toward the upper end — or beyond — for peak-season Gulf arrivals (June–September) and for very damp goods such as green timber, leather or cotton.

Correct Placement and Handling

• Hang units from the container's side-wall lashing rings, spaced evenly along the load, at roughly knee-to-chest height.
• Keep 10–15 cm clearance from the cargo so air can reach the desiccant.
• Place at least one unit near the doors — the coldest surface on arrival, and where condensation drips.
• Inspect units before loading: never load a bag that is already swollen, wet or leaking.
• Do not puncture the bag; the brine inside is harmless to cargo only while contained.

Common Mistakes

• Under-dosing — the most expensive error; a claim costs far more than extra units.
• Assuming the container is sealed — constant air exchange defeats any desiccant. Inspect door seals.
• Stacking all units in one corner — defeats even distribution.
• Using saturated desiccant — spent units absorb nothing.