Moisture damage 101 – What is moisture damage?

Article updated: 2025-07-03

Causes, risks and moisture damage prevention in cargo shipping

In the first of several of guides, we lift the lid on the world of moisture prevention. Moisture 101 introduces beginners to the basics and how to get them right. But we hope it’s also a helpful refresher for those of you with more experience. Enjoy!

If you’re shipping rubber ducks then you can stop reading now. Go outside, enjoy yourself, live in the moment, the world’s your oyster etc.

But for everyone else and almost every other cargo, we need to know our enemy: Moisture. And it’s a sneaky enemy too, causing all kinds of damage to goods – directly through corrosion or mould etc. and even indirectly by ruining packaging that protects against scratches, scrapes or squashes … wait, is it too late to get the rubber duck guys back? They’re gone? Oh well.

In this blog article, we’ll cover the different types of moisture damage, including those that can affect the goods you are most interested in. We hope it’ll be a useful guide to the risks you should be aware of and protect against. And, by minimizing these risks, it should also save yourself and your business a lot of extra cost and hassle.

A simple definition of moisture damage

Moisture damage refers to any harm or deterioration that occurs to cargo during shipping as a result of excess moisture. This typically happens due to condensation inside the container (commonly known as container rain) or prolonged exposure to high relative humidity during transit.

Why is relative humidity so important?

Before we start looking at the most common types of moisture-related damage, first an explainer for a term that always comes into play: Relative humidity.

Relative humidity or RH describes how much moisture is in the air at a certain temperature. And this is what you need to keep an eye on as it’s when relative humidity reaches a certain percentage in a container that it will cause damage to goods – and that damage can increase exponentially when RH goes even higher.

The most common types of moisture damage are:

Corrosion

Metal parts can corrode and rust, which can weaken metal, cause discoloration or, in the case of expensive electronics, make them utterly useless. An RH of around 45% or less shouldn’t be a problem. But at 60% or more, your metal goods and any metal parts will probably be in trouble.

You can read our whitepaper on corrosion prevention to learn how to protect your cargo from this common and costly type of damage.

Mould and mildew and bad or changed smell or taste

Mould and mildew can affect all cargo and its packaging. And that’s a particularly nasty problem for organic cargo like food or agricultural commodities. To make matters worse, moisture damage can also affect the smell and taste of food. Which even less fussy eaters tend to get picky about.

A relative humidity over 75% means that mould can grow in any temperature between -5 °C and +55 °C – and mould’s favourite temperature is a very normal 20-30 °C!

Research also shows that mould could even be a problem with an RH as low as 50%.

So anyway, you look at it, if you want to protect cargo, especially organic goods that aren’t deep frozen, you will need to ensure lower levels of moisture in the container

Damaged packaging , collapsed packaging and peeling labels

As we mentioned at the top, moisture also causes indirect damage to goods by compromising packaging. Basically, traditional wood-fibre cardboard and similar want to absorb moisture from the air. If you want to impress friends and family, this quality is called hygroscopic.

Anyway, moisture damage to packaging means it can collapse and goods risk physical damage. Or with nice attractive packaging on the shelf being a key part of selling products in stores, the value of the product is greatly reduced and/or it may need to be returned for repackaging, which will waste a lot of time, money and good will throughout the supply chain.

Similarly, moisture can damage labels so they peel off from glass bottles and cans of food. And the market for random sauces and mystery cans of meat isn’t so hot at the moment.

Powder caking

Dry goods like powders are often hygroscopic – well, you’re an expert now – and will attract moisture. This moisture damage appears as caking or clumping. Which often means the powder won’t flow or mix as intended in use or during later stages of manufacturing. The result? An entire shipment may have to be scrapped or at least re-processed at great cost.

Real-world consequences of moisture damage

Moisture damage doesn’t just ruin products — it disrupts schedules, adds unexpected costs, and creates headaches across the supply chain. Damaged goods may need to be repacked, re-shipped, or written off entirely. Entire shipments can be rejected. And often, these losses aren’t covered by insurance.

That’s why preventing moisture damage isn’t optional — it’s essential to keeping cargo protected.

How to prevent moisture damage:

Moisture damage is preventable, but only if you take proactive steps before the container doors close. Below are some of the most effective ways to protect cargo from the invisible threat of excess humidity and condensation.

• Use of container or inbox desiccants or moisture absorbers

  Basically desiccants absorb (or adsorb) excess humidity from the air and help maintain safer levels of relative humidity during the shipping rip.

• Proper storage before shipping

  What happens before shipping is just as important as what happens during it. If your cargo sits in a damp warehouse or gets packed while materials are still moist, you’ve already started the journey with a disadvantage.
  Keep goods in dry storage conditions and double-check that pallets, packaging, and products are in good condition and dry before loading.

• Monitoring relative humidity

  It’s easier to control what you can measure. Using data loggers inside the container gives you real-time insight into humidity levels — when and where they spike, and whether your desiccants are doing their job. Plus, having this data on hand can help troubleshoot issues later.

• Container rain prevention

  You can’t stop the day-night temperature swings that cause container rain (unless you’ve got a climate-controlled container), but you can reduce the risk. Make sure everything going into the container, the cargo, the packaging, even the container walls, is dry. Don’t give moisture a head start. This whitepaper from the College of Natural Resources and Environment explains the main sources of moisture inside containers.

You can also read our next 101 guide on Container Rain to understand how condensation forms inside containers and how to prevent it.

Talk to us

And if you want to dig deeper into the specifics of your particular shipments, and find out where the biggest moisture damage risks lie and how to take the most effective and cost-effective prevention measures, then give us a call.

Yes, even if you’re shipping rubber ducks…