Moisture is one of the biggest threats to cargo during ocean shipping, and the damage it causes can be costly. Temperature changes throughout a voyage can create condensation inside sealed containers, leading to what is commonly known as container rain. The right container desiccant helps prevent that moisture from forming in the first place, protecting products from mold, corrosion, rust, and other humidity-related damage. Royco Packaging supplies Container Dri II® desiccants in a variety of formats to help businesses safeguard shipments and reduce the risk of moisture damage during transit.
What Is Container Rain?
Container rain is not rain from the sky. It is water that forms inside a shipping container and drips down onto the cargo below. When a container loaded in a warm, humid port moves through cooler waters or hits a cold front, the walls and ceiling cool down fast. The moisture in the air inside turns into water droplets on those cold surfaces. Those droplets gather, fall, and soak into whatever sits beneath them. Powders cake up. Metal parts rust. Labels peel off. Wood warps. Food and farm goods grow mold. This cycle repeats every time the temperature swings during a voyage that can last weeks.
Industry data puts moisture damage at about 12% of affected container loads. In a fleet of 1,000 containers, with each holding $25,000 worth of goods, that adds up to $3 million in lost cargo. The problem is common, but it is also preventable.
Why Moisture Develops During Ocean Freight
Warm air holds a lot of water vapor. When a container is packed near the equator in the middle of summer, that hot, damp air gets sealed inside. As the ship sails into cooler regions or the temperature drops at night, the container walls turn cold. When the surface temperature falls below the dew point, the air can no longer hold its moisture. Condensation forms, just like water beads on a cold glass on a summer day.
This does not happen just once. A container on a long ocean route goes through repeated heating and cooling cycles. Every swing brings a fresh round of condensation. The moisture builds up, and the damage worsens with each passing week.
How Shipping Container Desiccants Work
A shipping container desiccant pulls water vapor out of the air before it can turn into liquid on the walls. Instead of waiting for condensation to happen and then dealing with the mess, desiccants stop the problem at the source. They keep the air dry enough that the dew point stays below the temperature of the container surfaces. No dew point crossing means no container rain.
How Container Dri II Lowers the Dew Point
Container Dri II, made by Clariant, takes a direct approach. It actively lowers the dew point temperature inside the container and holds it below the temperature of the walls and ceiling. When that gap stays in place, condensation never gets the chance to form.
The active ingredient is calcium chloride, a compound that grabs moisture far more aggressively than traditional silica gel, especially in the high-humidity conditions found in tropical shipping lanes. As it absorbs water vapor, the calcium chloride changes from dry granules into a thick, stable gel. There is no liquid runoff. No dripping. No risk of the absorbed moisture leaking back out when temperatures rise again. Once the moisture is locked in, it stays locked in.
The absorption numbers tell the story. Under tough conditions, 95% relative humidity at 40°C, a single 125-gram bag soaks up roughly 500 grams of water. That is more than 400% of its own weight. Silica gel, by comparison, tops out around 20 to 30% under normal conditions. At the humidity levels where container rain becomes a real threat, the performance gap between the two is wide.
The Federation of Cocoa Commerce specifically recommends calcium chloride desiccant for container shipments of cocoa beans, with a minimum loading of 65%. Container Dri II meets and passes that bar.
Available Types and Configurations
Container Dri II comes in several formats, each built for different loading needs. Royco stocks multiple types and can help you pick the right one.
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Pole Format (500g, 750g): A rigid hanging bag that suspends from the eye hooks inside a shipping container. Hanging the desiccant high, near the ceiling where warm, moist air gathers, puts it in the best spot for dew point control over a long trip.
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Container Dri II Plus (1,500g): Large bags with built-in carabiners that clip straight onto container eye hooks. Fewer pieces to handle during loading. Three bags cover a 20-foot container. Six bags cover a 40-foot container. A good pick when loading speed matters or when you are shipping in high volumes.
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Hard-Shell Pack: A rigid case that can hang or mount to a surface. The shell keeps the desiccant away from direct contact with cargo and makes cleanup at the destination quick and simple.
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Individual Bags with Adhesive Backing (125g, 140g): Flat bags with peel-and-stick strips. Stick them right onto container walls or pallet sides. Works as a primary solution for smaller loads or as extra protection around sensitive cargo inside a larger container.
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Adhesive Strip Format: A wall-mount strip design for setups where hanging is not an option. Sticks to metal, wood, and corrugated surfaces.
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Blanket Format: A flat desiccant blanket that sticks to cargo surfaces or cardboard slipsheets. Gives even coverage across flat pallet loads of sensitive goods.
How Many Desiccant Bags Are Needed?
The right count depends on your container size, the type of cargo, how long the trip will take, and how humid the origin port is. As a general starting point, a 20-foot container often needs about 3 to 4 bags of the larger formats, while a 40-foot container takes roughly 6 to 8 bags. Smaller individual bags are used in higher numbers depending on the load.
These are rough guidelines, not fixed rules. Royco's team can walk through your specific shipment details and give you a solid recommendation. Getting the number right means no wasted product and no gaps in coverage.
Placement and Installation
Where you put the desiccant matters almost as much as how much you use. Warm, humid air rises, so the best spot is high up near the container ceiling. Hanging formats clip right into the eye hooks already built into the container walls. Adhesive formats peel and stick to the wall surface. Most setups take under two minutes per bag to install.
When the voyage ends, the spent bags contain a solid gel. They can go out with regular industrial solid waste. No special handling, no hazardous materials paperwork, no extra disposal fees at the destination port.
Applications by Cargo Type
Container Dri II is non-toxic, free of Dimethyl Fumarate (DMF), and meets FDA standards for direct contact with food and drug products. It protects a wide range of cargo.
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Agricultural Goods: Coffee beans, cocoa beans, grains, nuts, and spices stay dry and mold-free. The Federation of Cocoa Commerce guidelines specifically recommend calcium chloride desiccants for cocoa shipments.
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Food and Beverages: Canned goods, packaged foods, and dry ingredients keep their labels and their quality intact.
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Pharmaceuticals and Nutraceuticals: Sensitive products that need stable conditions arrive without moisture damage.
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Electronics and Auto Parts: Circuit boards, connectors, and metal components stay free of rust and corrosion.
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Powders and Bulk Chemicals: Dry powders stay dry. No caking, no clumping.
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Furniture and Wood Products: Wood avoids warping, swelling, and mold growth.
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Glass, Ceramics, and Machinery: Surfaces stay clean, and metal parts avoid rust during long transits.
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General Manufactured Goods: Any product that ships in a sealed container can benefit from controlled humidity.
For defense and government contractors, Container Dri II works in any container shipment where moisture protection is called for but no specific military packaging rule governs the desiccant format.
Frequently Asked Questions
How is calcium chloride different from silica gel for cargo?
Calcium chloride absorbs far more moisture, up to 300% or more of its own weight, compared to 20 to 30% for silica gel. It also locks moisture into a gel that does not release back into the air when temperatures rise. Silica gel can release moisture during the heating cycles of a long voyage, right when condensation risk is highest.
Is Container Dri II safe for food shipments?
Yes. It meets FDA standards for direct contact with food and drug products and is free of Dimethyl Fumarate (DMF).
How do I know which format to choose?
It comes down to your loading setup. If your containers have eye hooks, pole or carabiner formats are the most effective because they hang high near the ceiling. If hooks are not available, adhesive strips or blanket formats work well. Royco can help you match the format to your operation.
How do I figure out how many bags to order?
The key factors are container size, cargo sensitivity, voyage length, and origin port humidity. A standard 20-foot container often uses 3 to 4 larger bags, and a 40-foot uses 6 to 8. Smaller bags are used in higher counts. Royco's team can give you a specific recommendation based on your shipment.
How do I dispose of used desiccant bags?
Fully spent bags contain a solid gel and can go in regular industrial solid waste. No special waste stream or hazardous materials handling is needed.
Does Container Dri II carry any sustainability certifications?
Yes. It holds the Clariant EcoTain label, given to products with verified sustainability benefits across their full lifecycle. This can support responsible procurement and ESG reporting requirements.
Request a Quote
Stop container rain before it reaches your cargo. Royco Packaging stocks Container Dri II in multiple formats and ships from Huntingdon Valley, PA. Whether you need a quote, help picking the right size and format, or a recommendation based on your shipping route, a real person will answer when you reach out.
Call: 1-800-677-6926
Email: sales@roycopackaging.com
Website: roycopackaging.com
Container Dri® is a registered trademark of Clariant, registered in many countries. Royco Packaging, Inc. is an authorized distributor.