Hey everyone, it’s Jake here, from the coextruded film team that’s actually on the ground problem-solving for our clients — the ones who call us when their packaging’s carbon dioxide (CO2) barrier is dropping and their products are spoiling too fast. Let’s cut to the chase: if you’re reading this, you’re probably tired of vague, textbook answers about why your coex film isn’t holding CO2 like it should, or you’re new to the game and trying to figure out what actually makes these films work for things like craft beer, sparkling seltzers, or even fresh snacks that need to keep their fizz locked in. I’ve spent the last 7 years troubleshooting these films, testing every tweak to our line, and chatting with 100+ brand owners who’ve dealt with costly spoilage or bad product reviews because of bad barrier. So today, let’s break down the real, actionable factors that kill or boost a coextruded film’s CO2 barrier — no stuffy PhD jargon, just what I see on the shop floor and in client labs. Coextruded Film
First, let’s get one thing straight: coextruded films aren’t just one plastic. They’re like a sandwich — multiple layers of different polymers, each with a job. The core here is that the layers that make up the film stack are the biggest piece of the CO2 barrier puzzle. You can’t throw any plastics together and expect good barrier, plain and simple. Let’s start with the biggest culprits (and secret weapons) here: material selection. I’ve had clients come to me saying “we used X plastic, why’s the CO2 leaking?” — nine times out of ten, it’s that they picked a polymer that’s actually super permeable to CO2. Wait, permeable? Yeah, that means gas passes through it, like how air leaks through a balloon. The “good” barrier polymers are the ones with tight molecular structures that CO2 can’t slip through easily. Things like EVOH (ethylene vinyl alcohol) — that’s our go-to core barrier layer for most high-demand products. But here’s the thing about EVOH: it’s super sensitive to moisture. If EVOH gets wet, its molecules loosen up, and CO2 can zip right through. That’s why we always pair EVOH with a moisture barrier layer, usually polyamide (PA) or a tie layer that keeps water out of the EVOH. I once had a craft beer client who was using a film with EVOH exposed directly to humid ambient air during transport — their CO2 retention dropped 18% in 2 weeks, no lie. They switched to our standard EVOH-PA core, and that number went back up to 97% retention, exactly what they needed. Not all EVOH is created either — there’s different grades, right? Lower EV content EVOH is more flexible, but higher EV content is way better for CO2 barrier. We don’t skimp on that, because I’ve seen the cost-savings from lower grade bite clients in the end. Then there’s the alternative if EVOH isn’t an option: PVDC (polyvinylidene chloride). It’s been around longer, still works great, but it has its own issues — like being harder to recycle, which is a big deal for brands these days. We offer PVDC-based films too, but most of our newer clients lean toward EVOH because of sustainability, as long as their application doesn’t have weird humidity conditions.
Next up: layer thickness and uniformity. This is a make-or-break factor that a lot of clients don’t realize until their first roll of film arrives and they test it. If your barrier layer is too thin, there’s just not enough of the tight molecular structure to stop CO2. Simple math, right? More barrier layer = better barrier — up to a point, anyway. But you can’t just crank up the thickness willy-nilly, because too thick makes the film stiff, hard to seal, and more expensive. What’s way trickier is uniformity. If one part of the roll has a barrier layer that’s 10 microns thick and another spot is 6 microns, you’ve got weak points where CO2 can leak through. We’ve got in-line thickness monitoring on all our lines now — it’s a $500k investment, but it’s saved us from so many bad rolls that would’ve gone out. A while back, a snack brand got a bad batch from another supplier, their chips went stale because of uneven barrier, and they switched to us because we had the data proving every inch of their film stack was within 0.5 microns of the target. Layer uniformity also ties into how we coextrude the layers — if the molten polymers don’t mix properly at the interface, you get gaps between layers, which is another entry point for CO2. That’s why we use custom tie layers for every blend, not the generic ones you can buy off the shelf. Generic tie layers might work for a single application, but for something like a multi-layer film for carbonated drinks, you need a tie layer that actually bonds the EVOH and PA so there’s zero gaps.
Third big factor: processing conditions during production. This is the stuff that happens in our shop, not in the client’s facility, but it makes or breaks the final product. Let’s talk about melt temperature first. If we heat the barrier polymer too hot, it can start to degrade — molecules break down, get smaller, so CO2 can slip through way easier. If we don’t heat it enough, it doesn’t flow properly, so we get voids or gaps in the barrier layer. We track melt temp every single minute on every line, and adjust for humidity in our warehouse too, because even the air around the extruders affects the polymer. Then there’s cooling rate. When we extrude the film, we cool it down quickly, that locks the polymer structure tight, right? If we cool it too slowly, the molecules can rearrange into looser, more permeable shapes. I once ran a trial for a sparkling water brand where we messed up the cooling zone by 5 degrees — their CO2 barrier was 22% lower than the target. Fixed the cooling, and we hit the mark on the dot. Also, cast vs blown coex? Wait, we do both, depending on what the client needs. Cast films are flatter, more uniform, so barrier is a little more consistent, while blown films are more flexible, good for pouches. But the processing differences still apply — you can get good barrier either way, you just have to adjust the temp and speed for each line. Don’t even get me started on tension during winding. If you wind the film too tight, you stretch the layers, create micro-cracks in the barrier — boom, CO2 leaks. Too loose, and the layers shift. We measure tension across the entire roll, not just at the ends, so every meter is perfect. I’ve had trainees mess that up and ruin a 10,000 foot roll — cost us a few grand, but it taught us to never skip that step.
Then there’s post-production handling and testing, wait — that’s not just our job, it’s the client’s, but it affects how the film performs. No matter how good our film is, if the client mishandles it, they’ll get bad barrier. Let’s say they store the film in a hot, humid warehouse for 3 months before using it — like I said earlier, EVOH soaks up moisture, barrier drops. Or if they’re sealing it wrong. Heat sealing is huge. If you over-seal, you melt the barrier layer, create holes. Under-seal, and there’s gaps along the edges. We send every client a seal profile guide specific to their film, because that’s one of the top reasons clients come back saying their barrier is off. We also recommend that they test for CO2 barrier before full production — use a coulometric test, not just a guess from the specs. A lot of clients just go by the printed barrier number, but that number is under ideal lab conditions. We give our clients real-world test data too, not just lab numbers, so they know what to expect when their product is sitting on a shelf in a grocery store in Florida, not a climate-controlled lab.
Wait, let’s not forget the elephant in the room: contaminants and defects. Even the best coex line can have a speck of dust, or a leftover piece of old polymer from a previous run, that gets into the film. That speck creates a pinhole, which is basically a direct pathway for CO2. We have 100% inline defect detection now, using cameras that spot even the tiniest pinhole, and we pull those rolls before they leave the warehouse. A few years back, we had a run where a cleaning rag fell into an extruder — we caught it mid-run, pulled the whole batch, fixed the line, and learned our lesson: no rags near the line, ever. We also filter every polymer layer before extrusion, remove any particulates, so they can’t make it into the final film.
Another thing I’ve noticed over the years: environmental conditions during storage and end-use. The film doesn’t exist in a vacuum, right? If your product is a sparkling beer that’s being shipped from Portland to Miami, where it’s hot and humid, that’s way harder on the film than if it’s sitting in a cooler in New York. Heat makes polymers more flexible, so CO2 moves through faster. Humidity breaks down EVOH, like I said. We actually do accelerated aging tests here, we expose films to high temp and humidity for a set time, test their barrier, so we can adjust the film stack for each region. We had a client in Brazil who was losing 10% CO2 after 3 weeks in transit, we swapped their standard EVOH for a higher grade EVOH and added an extra PA layer, and they only lost 2% in the same time. That’s the kind of tweak we do for every client, not a one-size-fits-all solution.
Wait, should I mention common myths? Like, “thicker film always means better barrier.” No, that’s not true. If you have a film with a 20 micron EVOH layer and a 50 micron outer layer, that’s better than a film with a 30 micron EVOH layer and a 50 micron outer layer. The barrier is almost entirely from the core barrier layer, the outer layers are for strength, sealability, etc. So wasting money on a thick outer layer is stupid, we tell our clients that all the time. Another myth: all coex films are the same. Nope, you can have two films with the same number of layers, same polymer types, but different processing, and their CO2 barrier can be 30% different. That’s why when clients ask for quotes, we don’t just give a price, we ask what their product is, where it’s going, how long it needs to hold CO2, because that changes everything.
Now, let’s wrap this up, because I know some of you are tired of reading, but if you’re still here, you’re the one we can help. The takeaway here is that CO2 barrier in coextruded films isn’t caused by one single thing — it’s a combination of material choice, layer thickness and uniformity, processing conditions, handling, and even the end-use environment. It’s not rocket science, but it’s the kind of detail that makes the difference between a product that sells and one that gets returned because it’s flat.
If you’re dealing with CO2 leakage in your packaging, or you’re launching a new product and need a film that can hold fizz, don’t guess with generic suppliers. We test, we tweak, we send you real data, and we don’t leave you hanging after delivery. Hit us up to talk through your project, no obligation, no pushy sales stuff — just us guys who know coex films, helping you get the barrier you need for your product.
Vacuum Skin Packaging Film REFERENCES
- Sørensen, P. O., & Jensen, L. (2018). Permeation of gases through coextruded polymer films: The role of layer structure and material selection. Journal of Packaging Science and Technology, 27(3), 189-205.
- Rooney, M. L. (2020). Moisture effects on ethylene vinyl alcohol (EVOH) barrier performance in flexible packaging. Packaging Technology and Science, 33(7), 291-302.
- Thompson, A. D., & Lee, S. H. (2021). Processing parameters and their impact on interlayer adhesion and barrier properties of coextruded blown films. Polymer Engineering & Science, 61(11), 2678-2687.
Sinosealed Packaging Solutions Limited
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