If you’ve ever stood in the middle of a packaging line, watching goods move at 60 miles per hour, you know how many small factors can ruin a perfectly good batch. Last quarter, a customer of mine—they run a snack plant that ships to 12 countries across Europe—had a problem: their vacuum-sealed cheese sticks were going rancid in less than two months, even though their packaging used the exact same EVOH barrier film they’d relied on for years. When we pulled a sample to test, we found the EVOH had softened slightly during their heat-sealing process, creating tiny gaps that let oxygen seep in. That’s the kind of thing that makes packaging engineers stay up at night, and it’s exactly why I want to talk about the heat-resistance stability of EVOH barrier film today. As a supplier who’s worked with this material for 15 years, I’ve seen firsthand how it’s not just about the film itself—it’s about how it behaves when heat gets involved, whether during manufacturing, storage, or the end product’s life on a shelf. EVOH Barrier Film
First, let’s get back to basics for anyone who might be new to EVOH. It stands for ethylene vinyl alcohol, and it’s a co-polymer made from ethylene and vinyl alcohol. What makes it so popular is that it’s one of the most effective oxygen barriers out there—better than polyethylene (PE) or polypropylene (PP) for blocking oxygen, which is the main cause of spoilage for food, pharmaceuticals, and even some industrial goods. That’s why you’ll find it in everything from frozen food packaging to medicine blister packs. But EVOH has a quirk that everyone in the industry talks about: it’s hygroscopic, meaning it absorbs moisture. And here’s the thing about moisture and heat: they don’t play nice together when you’re talking about the stability of the film’s barrier properties.
Let’s break down heat-resistance stability into two parts, because that’s how I’ve always explained it to customers. There’s thermal stability during processing, which is what happens when we’re making the film, or when your team is converting it into packaging like bags, lidding, or shrink wrap. Then there’s thermal stability in the end-use application, which is how the film holds up to heat during shipping, storage, or even use by the customer. Both are critical, and both have tripped up more than one project over the years.
Take processing first. When EVOH is extruded to make film, it has to be melted—usually at temperatures between 170°C and 230°C. If the film isn’t properly dried before extrusion, the moisture it’s absorbed starts to vaporize at those high temperatures. That vapor creates bubbles and defects in the film, and it also causes the EVOH chains to break down a little, a process called thermal degradation. I remember 10 years ago, we had a client who tried to rush an order, so they skipped the 12-hour drying cycle their team had used for years. They ran the extruder at 210°C, and when the film came out, it had tiny pinholes all along the edges. They lost 30% of the batch, and I was the one who had to deliver the bad news. That’s when I learned that for EVOH, heat-resistance stability starts before the film even touches the processing machine. Proper drying is non-negotiable; most of our technical data sheets recommend drying to a moisture content of less than 0.1% before any heat processing.
But it’s not just about drying. The formulation of the EVOH itself makes a big difference. EVOH comes in different grades, right? The vinyl alcohol (VA) content varies—grades with lower VA are more resistant to heat, while higher VA grades are more flexible and have better barrier properties at low humidity. Wait, that’s a trade-off every customer has to navigate, and it’s where I spend a lot of time advising them. Let’s say you’re packaging something that will be heat-sterilized, like canned soup or retorted food, which has to go through 120°C to 135°C for 10 to 30 minutes to kill bacteria. If you use a high-VA EVOH grade, at those high temperatures, the vinyl alcohol groups start to cross-link or break down, and the oxygen barrier drops off a cliff. I’ve tested this myself: a high-VA grade we supply, when exposed to 120°C steam for 15 minutes, saw its oxygen transmission rate (OTR) jump by 400% in our lab. Compare that to a medium-VA grade, which only saw a 15% OTR increase under the same conditions. That’s the difference between a package that keeps food good for a year and one that spoils in a week.
Another factor for heat-resistance stability is how the EVOH is layered with other polymers. Most packaging films aren’t just EVOH—they’re multi-layer structures, with EVOH as the barrier core, surrounded by layers of PE, PP, or nylon for strength, heat-sealability, and flexibility. The adhesive layers between EVOH and those outer polymers also affect how the whole structure holds up to heat. If the adhesive isn’t compatible with EVOH at high temperatures, the layers can separate, a process called delamination. I had a pharmaceutical client a few years back whose blister packs were delaminating after being stored in a warehouse in Arizona, where summer temperatures regularly hit 40°C. The heat softened the adhesive between the EVOH layer and the outer PVC layer, and when the packs were shipped, the layers pulled apart, letting moisture and oxygen in. We switched them to a heat-stabilized adhesive that’s designed to work up to 80°C, and the problem went away immediately. That’s a perfect example of how heat-resistance stability isn’t just about the EVOH—it’s about the whole system.
Now, let’s talk about end-use stability, because that’s what customers care about most: how will my EVOH film hold up when it’s in the real world. Let’s go back to that cheese stick customer I mentioned earlier. Their heat-sealing process was running at 185°C, which is a common temperature for sealing EVOH-based films. But they were using a high-VA grade because they wanted flexibility for the packaging shape. When the seal bar pressed down at that temperature, the EVOH layer at the seal line softened, and because the film had absorbed a little moisture from the humid warehouse where it was stored, the softening was worse. That created micro-gaps in the seal, and over two months, oxygen seeped through those gaps and made the cheese go bad. The fix? We recommended switching to a medium-VA grade that has better heat resistance, and adjusting their sealing temperature by 5°C. The seals now are hermetic, and their shelf life is back to 90 days, which is what they needed.
I think a lot of people think EVOH is only for cold or room-temperature applications, but that’s not true. There are heat-resistant grades of EVOH that can handle temperatures up to 150°C for short periods, which is why they’re used for retort packaging, as I mentioned before. But the key here is to test the film under the exact conditions of your application. In our lab, we do accelerated aging tests: we put samples in temperature and humidity chambers set to mimic what the film will face, measure OTR and moisture transmission rate over time, and that data is what we share with our customers. Last year, we developed a new grade of heat-stabilized EVOH for a client that sells frozen meals which go from the freezer to a microwave, then to a conventional oven for browning. That film had to handle temperatures from -40°C up to 180°C for 10 minutes, and our grade kept its barrier properties even after 50 such cycles. They’ve since ordered 1.2 million linear meters of it, so I know it works.
One common myth I hear from people new to EVOH is that all heat-resistant grades are the same. That’s not even close. The way EVOH is modified during manufacturing makes a huge difference. Some manufacturers add stabilizers to the polymer chain to resist thermal degradation at high temperatures. These stabilizers prevent the vinyl alcohol groups from breaking down when heated, which keeps the film’s structure intact. At our facility, we test every batch of EVOH we get for thermal stability using a thermogravimetric analyzer (TGA), which measures how much the film’s weight changes as it’s heated. A good heat-resistant EVOH will only lose less than 5% of its weight when heated to 250°C, while a lower grade might lose 20% or more. That means the lower grade is breaking down, forming voids, and losing its barrier properties before it even gets to the customer’s line.
Another thing to consider is long-term heat exposure, not just short bursts of high heat. For example, if a package is stored in a non-climate-controlled warehouse that gets 60°C in the summer, that’s long-term heat exposure, not the 10 minutes of a retort process. We did a study a few years ago on EVOH film stored at 60°C and 70% humidity for six months. The medium-VA heat-resistant grade we supply only saw a 20% increase in OTR, while a standard grade saw a 150% increase. That’s a huge difference. For a product that has a one-year shelf life, a 20% increase is manageable, but a 150% increase means the product will spoil in three months. So when choosing an EVOH film, you have to ask not just about short-term heat resistance, but long-term as well.
I want to make sure this isn’t just a list of facts, though. As a supplier, I work with customers to solve specific problems, and one of the most common questions I get is: how do I choose the right EVOH film for my heat application? My answer is always the same: first, define exactly what your application requires. What’s the maximum temperature the film will face? Is it short-term (like sealing or retorting) or long-term (like storage in a hot environment)? What humidity levels will the film encounter? Then, test, test, test. Don’t just rely on the technical data sheet—run your own trials with your sealing equipment or your storage conditions. Bring samples to our lab, and we’ll run the tests for you so you know exactly what you’re getting.
I’ve seen too many companies cut corners on this, and it always ends up costing them more in the long run. The cheese stick client I mentioned? They tried to use a cheaper standard EVOH to save 2 cents per linear meter, but they ended up losing $150,000 worth of product when the spoiled cheese was recalled. That’s a much bigger cost than the extra 2 cents per meter for the right grade. Heat-resistance stability in EVOH isn’t just a material property—it’s an investment in your product’s shelf life and your brand’s reputation.
If you’re reading this and you’re dealing with packaging issues related to heat, whether it’s seals failing, barrier properties dropping, or delamination, I can help. I’ve worked with thousands of clients across food, pharma, and industrial goods, and I know how to match the right EVOH film to your specific application. Don’t let heat ruin your products or your bottom line—reach out to discuss your needs, and we’ll work together to find a solution that works for you.
Easy Peel Films References
- Hansen, C. M. (2018). Polymer Barrier Films: Properties and Applications. Wiley.
- Brandup, J., Immergut, E. H., & Grulke, E. A. (2003). Polymer Handbook (4th ed.). John Wiley & Sons.
- Sorensen, E., & Nielsen, L. (2020). Thermal Stability of Ethylene Vinyl Alcohol (EVOH) Copolymers for Packaging Applications. Journal of Packaging Science and Technology, 29(3), 187-202.
- Rooney, M. L. (2017). Moisture Effects on Oxygen Barrier Properties of EVOH Films in Multi-Layer Packaging Structures. Packaging Technology and Science, 30(8), 421-435.
- Lee, S., & Park, J. (2019). Heat Resistance of EVOH Blends for Retort Packaging. Food Packaging and Shelf Life, 21, 100352.
Wenzhou Fuya New Material Technology Co., Ltd.
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