If you’ve ever ordered fresh produce that arrived limp days ahead of its shelf life, or struggled with a batch of shrink-wrapped industrial parts that developed rust long before they reached the customer, you’ve encountered a gap in gas barrier performance. As a shrink film supplier, one of the most common questions I get from packaging engineers and quality control (QC) managers isn’t just “what’s your film’s oxygen rating?”—it’s “how do I know that number is accurate?” Shrink Film
For years, I watched customers test shrink films in random, inconsistent ways: leaving rolls out in a warehouse for a week to guess degradation, punching holes in samples and using a homebrewed oxygen tester, or taking lab results at face value without understanding how those results translate to real-world packaging. The truth is, measuring shrink film’s gas barrier isn’t a one-size-fits-all process. It depends on what you’re packaging, your production environment, and even how you plan to heat and seal your film. After 12 years in this business, I’ve walked hundreds of clients through this process—and the mistakes they’ve made have taught me far more than any textbook ever did about getting it right.
First, let’s get one thing straight: gas barrier for shrink films isn’t just about resisting oxygen. It’s also about carbon dioxide, water vapor, and even nitrogen, depending on your application. A food manufacturer packing roasted coffee needs high oxygen and CO2 barrier to keep the beans fresh, while a pharmaceutical company packaging sterile syringes needs water vapor barrier to prevent moisture damage, and an industrial customer shipping sensitive electronics might need all three. But the core principles for measurement stay the same—if you follow them, you’ll avoid costly failures down the line.
Start with the basics: understanding what “barrier” actually means for shrink film, not just flat film. Flat films and shrink films use the same polymer bases (most often polyethylene, polypropylene, polyester, or EVOH, the gold standard for high barrier), but shrink films undergo a critical stretching step during manufacturing. That stretching aligns the polymer molecules, which changes not just the film’s shrinkage rate and clarity, but its gas permeability too. I once had a client who switched from a flat film they’d used for years to our shrink film because it was cheaper, but their oxygen readings were 3x higher than expected. It turned out they used the flat film’s standard permeability number for comparison, not accounting for how our shrink’s biaxial stretching tightened the polymer structure—so it had better barrier than the flat film, not worse. That’s the first rule: always test shrink film as it is, not as its un-stretched precursor.
Now, the two most common gases to measure are oxygen and water vapor, so let’s break those down, step by step, with real-world examples from my work.
For oxygen transmission rate (OTR) testing, the gold standard method per ASTM D3985 (the international standard for flexible packaging) is what’s called the coulometric sensor method. Here’s how it works, in plain terms: you take a precise-sized sample of your shrink film, mount it between two gas chambers. One side is flooded with a fixed concentration of oxygen, the other with a carrier gas (usually nitrogen). Any oxygen that passes through the film moves into the carrier gas, which flows to a detector that counts every oxygen molecule. The result is measured in cc (of oxygen) per 100 square inches of film per day, at a specific temperature and relative humidity (RH)—two factors that make a huge difference.
Wait, temperature and RH? That’s not just random numbers. I had a craft brewery client a few years back who tested our shrink film in a cold, dry warehouse and got an OTR of 0.2 cc/100in²/day—perfect for their cans, which need to stay fresh for 12 months. But when they moved their testing to their packaging line, which heated the film to 200°F and had 60% RH, the OTR jumped to 1.1 cc/100in²/day. That was a problem. Why? Shrink films’ polymer structure loosens when heated, and moisture can penetrate tiny gaps between polymer layers. So the test conditions have to match how you’ll actually use the film. If you’re packaging frozen food, test at 0°F; if you’re packing fresh bread, test at 70°F and 80% RH. Never trust a test that’s run at 73°F and 50% RH (the default for many generic tests) if that’s not your operating environment.
A cheaper alternative to coulometric testing is the pressure sensor method, used by some small labs and even home testing kits, but it has a big catch: it’s less accurate for high-barrier shrink films, where oxygen transmission is very low. For example, a film with an OTR of 0.1 cc/100in²/day might take 10 days to get a reliable reading with the pressure method, and any tiny leak in the sample mount will skew the result. Over the years, I’ve seen clients waste thousands on bad shipments because they used this method to cut corners. My advice: if you’re testing a high-barrier film for food or medical use, stick to ASTM D3985 and a coulometric tester. For low-barrier films used for, say, non-sensitive hardware, the pressure method might be fine—just make sure you add a 10% error margin to your results.
Now, water vapor transmission rate (WVTR), which is critical for products like dried fruit, pharmaceuticals, and electronics that can get ruined by even a little moisture. The standard here is ASTM E96, and the most common method is the cup test, which sounds simple but is full of pitfalls for shrink films. Here’s how it works: you take a small cup, fill it with a desiccant or water, seal your film over the top, put the whole thing in a controlled temperature/RH chamber, and weigh it over time. The change in weight tells you how much water vapor passed through the film.
But again, shrink film-specific tricks: when you heat and shrink film around a package, the film is stretched tighter than it is in the lab sample, which can change WVTR. I learned this the hard way with a client packing electronic circuit boards. They tested our shrink film flat, got a WVTR of 0.5 g/100in²/day, which seemed perfect. But when they shrank the film around the boxes, the WVTR dropped to 0.2 g/100in²/day—so their boards stayed dry, even when we’d warned them that tight shrinkage could reduce water vapor flow. That’s why I always advise clients to test their film in the “final form”: shrink it to the same tightness they’ll use in production, then test it, not just the flat sheet. Another common mistake with the cup test: not accounting for the film’s surface area. If your lab cuts a 100 in² sample, but your actual package uses 80 in² of film, you have to adjust the result—otherwise you’ll overestimate how much moisture can get in.
For applications that need to resist multiple gases—like modified atmosphere packaging (MAP) for fresh meat, which uses a mix of oxygen, CO2, and nitrogen—you need a different test: gas permeability coefficient, or “P-value”. This measures how much of a specific gas moves through the film, independent of thickness. Shrink films are often made in different thicknesses (from 1 mil to 10 mil, for example), so a P-value lets you compare films of different thicknesses fairly. For example, a 2 mil film with a P-value of 0.05 cc·mil/100in²·day·atm is more barrier than a 3 mil film with 0.08, even though the thinner film has a higher OTR when measured directly. For MAP applications, this is non-negotiable—we always provide P-values for clients so they can choose the right thickness for their product without sacrificing barrier performance.
Now, let’s talk about the real-world part: what do these numbers actually mean for your bottom line? I had a produce client a while back who switched to a lower-priced shrink film, convinced all films with an OTR below 2 cc/100in²/day were the same. Within six weeks, 20% of their spinach shipments were rotting before they reached grocery stores. When we tested their new film, it had an OTR of 1.8 cc/100in²/day at 40°F—but that number was for flat film, not shrink film. When we shrank it to their production specifications, the OTR jumped to 3.2 cc/100in²/day, which let too much oxygen in and too much moisture out. That cost them $12,000 in a single shipment, not to mention their reputation with grocery chains.
So here’s my three-step process for any client testing shrink film, developed over years of fixing these mistakes:
First, define your needs before you test. If you’re packing frozen pizza that will sit in a supermarket freezer for 6 months, you’ll need an OTR below 1 cc/100in²/day at 0°F and 50% RH. If you’re packing toy parts that just need dust protection, you might only need a low-cost film with an OTR over 100 cc/100in²/day. Don’t test for a higher barrier than you need—it’ll just cost you money.
Second, test the film as it will be used. That means: 1) use the correct temperature and RH for your packaging environment, 2) test the film after it’s shrunk to your desired tightness, not just flat, and 3) use the right test method for your application (coulometric for high-barrier OTR, cup test for WVTR, P-value for multi-gas needs).
Third, ask for third-party verification. A lot of film suppliers will give you their own test results, which are usually accurate (we always do, for what it’s worth), but a lot of them are also run at ideal conditions that don’t match your operation. Getting an independent test from a lab that specializes in flexible packaging will cost a few hundred dollars, but it’s way cheaper than a shipment of spoiled goods or failed product recalls.
Over the years, I’ve seen too many companies cut corners on barrier testing because it feels like a small detail. But shrink film’s gas barrier is what makes your packaging work—whether that’s keeping a bottle of wine’s flavor intact, preventing car parts from rusting, or making sure a batch of pharmaceuticals is safe to use. It’s not just a number on a spec sheet; it’s the difference between a product that reaches the customer as intended and one that ends up in a landfill, or worse, causes a customer complaint.
If you’re currently testing your shrink film and finding results that don’t line up with your product’s performance, or you’re shopping for a new film and not sure what numbers you actually need, I’ve helped dozens of teams work through this. I don’t push you to buy the most expensive film, just the one that fits your needs. The worst thing we can do as suppliers is oversell a film’s barrier or underdeliver, and that’s why I take the time to walk every client through testing step by step, not just give them a spec sheet.
So if you’re tired of guessing about your shrink film’s gas barrier, or you’ve had a bad experience with testing that didn’t match real life, reach out. We can walk through your specific product, your production process, and help you figure out exactly what testing you need to get reliable, usable results that keep your products safe and your customers happy.
Plastic Film References
ASTM D3985, Standard Test Method for Oxygen Gas Transmission Rate Through Plastic Film and Sheeting Using a Coulometric Sensor.
ASTM E96, Standard Test Methods for Water Vapor Transmission of Materials.
Robertson, G. L. (2016). Food Packaging: Principles and Practice (4th ed.). CRC Press.
Sorensen, G., & Piggott, M. R. (1990). Gas Barrier Polymers for Packaging. Journal of Plastic Film and Sheeting, 6(3), 222–241.
Xiamen Leadkit Group Co., Ltd.
Xiamen Leadkit Group Co., Ltd. is one of the most professional shrink film manufacturers and suppliers in China, specialized in providing high quality customized service. Please feel free to wholesale cheap shrink film from our factory. Contact us for more details.
Address: No.398, Jiahe Road, Huli District, Xiamen, Fujian, China
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