Will a sealed plastic bag protect my goods from moisture damage?
Three bananas wrapped in plastic film

Will a sealed plastic bag protect my goods from moisture damage?

Yes. No. Um… maybe?  

Sorry! Life is complex enough and we would love to give you a simple answer so we can all move on. But if you ship goods in plastic you need to hang around for a couple of minutes as we break down what you need to know to address the question. And maybe, right at the end, there is a simple answer: Leave it with us. Because giving you the right solution for your goods — and your unique moisture damage prevention needs — is what we do at Absortech. 

Many goods are shipped with sealed plastic protection. Whether to protect valuable cargo from dust or dripping water. Or also, in the case of electronics, automotive parts and similar, because it is seen as the first line of defense against corrosion by preventing excess moisture from acting on critical metal surfaces and circuitry. 

But to know whether sealed plastic packaging is really protecting your goods from moisture damage, you need to check off the following, smaller questions one by one. Because a plastic bag might be causing more problems than it solves, still leaving you and your shipments exposed to unnecessary and very costly risk. 

Plastic film bag not sealed

1. Is your sealed bag really sealed?

This might seem a stupid question but most people think plastic bags are total barriers. In reality plastic bags breathe – including dedicated VCI plastic protection against metal corrosion!

Performance is not indicated by the thickness of the plastic barrier but its MVTR (Moisture Vapor Transmission Rate). Measured in g/m²/24 hours or g/100 in²/24 hours, the MTVR shows how much moisture can enter a plastic bag during one day. A low MVTR means very little moisture can enter so a barrier like aluminum foil laminate is down to 0.001 g/m²/24 hours and a normal LDPE bag might be as high as 16-23 g/m²/24 hours.

MTVR is calculated with very high humidity on the outside of the barrier and zero humidity to start with on the inside. So it doesn’t mean up to 23 g of moisture per day in normal shipping conditions. But it often means a damaging amount of moisture that needs to be taken into account, especially over long transits.  

2. Are you sealing in excess humidity?

If the relative humidity in the packaging area was high, then the air sealed in the bag already has a high moisture content. Which often means a much higher risk for your product. 

3. Are you sealing in goods that release moisture?

When you’re at the supermarket, you’ve probably noticed that fresh goods like tomatoes or grapes are in plastic bags and containers with holes. This is because these foods are hygroscopic and can release moisture when the temperature goes up. Then, when the temperature goes down again, that moisture would condense within a sealed bag and start to damage the food. Hence the holes to release moisture and not trap it on the inside.  

So putting products and materials with moisture content (not just organic goods like fruit but even things like shirts and shoes that contain moisture) in a sealed plastic bag is asking for trouble. The risk of water condensing, pooling and damaging the goods is just too high. 

In-box desiccants in a box that contains products in plastic bags

4. Do you need in-bag desiccants for extra protection and peace of mind?

One solution to cope with excess moisture in the bag – whether it’s due to humid air sealed in, the plastic’s permeability or the moisture from the products itself – is to use desiccants in the bag. Of course, that will take extra time and money but certainly helps reduce the risk and helps you sleep better at night. But perhaps there are better overall solutions? 

5. Do you need to manage container humidity?

A better, more cost-effective solution than desiccant pouches in each bag is often to manage container humidity and remove a major underlying cause. If done effectively enough, you might even avoid using plastic altogether.  

6. Is plastic the most sustainable choice?

Beyond finding the most effective solution, it’s also very important for us and our customers to find the most sustainable solution. The good news is that better performance normally means better for the planet too because less desiccant or plastic can be used. Certainly, there are better and more sustainable alternatives instead of just relying on plastic as your moisture barrier.   

Worker checking his laptop in a warehouse

7. Are you 100% confident that you have the best solution?

As we go through these questions, you can see that new parameters are added and the choice appears more complicated. But that’s all part of the process as you identify the best solution for you, your goods and the environments they are shipped in.

We’ve made the complex simple by putting everything into our Peace of Moisture Mind approach where we measure and address the key areas. All with the goal of clearly identifying the best, most cost-effective and sustainable solution for each unique customer.   

So that’s the simple answer as promised. Just get in touch and have full confidence in your eventual solution – with or without plastic! 

To read more about anti-corrosion protection for electronics, automotive parts or other metal goods, then please download our white papers that really get into the issues and help you compare different solutions. For other industries and other plastic-sealed goods, don’t hesitate to ask us for our experience and any insights. 

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