What is the gas permeability of plastic film?

Hey everyone, thanks for swinging by my little corner of the internet—when I’m not geeking out over plastic films at work, I’m here to break down stuff I get asked nonstop by clients, new and old. Today’s topic is one that comes up all the time: gas permeability of plastic film. If you’re here because you’re looking for films for food packaging, medical supplies, or even industrial stuff, this is the lowdown you actually need, not the boring textbook jargon I used to sit through in college. Let’s dive in. Plastic Film

First, let’s keep it real—gas permeability isn’t just a random tech term. It’s basically how easily gases (think oxygen, carbon dioxide, nitrogen, even water vapor) pass through a plastic film. For most folks, this matters way more than you’d guess. Like, have you ever grabbed a bag of chips that’s still crisp a month later? Or a bottle of wine that tastes the same as the day you bought it? Or even a batch of fresh berries that doesn’t get moldy in three days? That’s all thanks to a film’s permeability. Mess that up, and you’ve got chips that go stale, medicine that loses its effectiveness, or produce that rots way too fast. And as someone who’s been supplying plastic films for over 10 years, I can tell you—this is one of the first questions I ask any new client before we even talk about pricing.

Let’s start with the basics that everyone gets confused about, because I’ve had so many clients mix these two up: permeability vs. permeance vs. perm-selectivity. Yeah, it’s a mouthful, but let’s keep it simple. Permeability is the inherent property of the plastic material itself—like how “porous” it is to gases, no matter the thickness. Permeance is permeability divided by the film’s thickness, right? So if you have a super thin film and a thick film made of the same plastic, the thick one will have lower permeance because the gas has to travel farther. Then there’s perm-selectivity—this is the cool part, where a film lets one gas through way easier than another. For example, a lot of food packaging films are selective to carbon dioxide, so CO2 (which helps keep food fresh) escapes slowly, but oxygen (which makes food go bad) is blocked. That’s the magic combo for snacks like pretzels or beef jerky.

Now, what actually makes a film permeable? I get this question all the time—why does one plastic let oxygen through, and another stops it cold? It comes down to how the plastic is structured, and it’s not as random as you might think. First, the polymer type is huge. Like, think of two common plastics we sell a ton: LDPE (low-density polyethylene) and EVOH (ethylene vinyl alcohol). LDPE is super flexible, used for things like grocery bags or bread wrappers—gas can slip through its loose polymer chains easy, so it’s high permeability. EVOH, on the other hand, has tighter, more ordered polymer chains that pack really close together, so gases can’t move through as well. That’s why EVOH is the go-to for films that need to block oxygen, like for meat packaging or pharmaceutical blister packs.

Wait, but there’s a catch with EVOH—its permeability changes a lot with moisture, right? If it gets wet, the polymer chains absorb water, which makes them loosen up, so oxygen can pass through way easier. That’s a thing we always warn clients about—you can’t use straight EVOH for frozen food, because frost would mess with its barrier. We usually laminate it with LDPE or another moisture-resistant plastic to fix that problem. That’s just one example of how even the most “barrier-heavy” films have tradeoffs, and knowing those is what makes all the difference for a good packaging solution.

Next up, thickness. Like I mentioned earlier, thicker films have lower permeance, but permeability stays the same because it’s a material property. But here’s the thing—you don’t always want a thicker film. Thicker stuff is more expensive, stiffer, and not great if you need flexibility. Like, if you’re making a bag for frozen veggies, you need a little thickness to hold up in the freezer, but you don’t want so much that it’s bulky and hard to seal. So it’s all about balancing thickness with the gas barrier you need. For example, a 1 mil (thousandth of an inch) LDPE film has an oxygen permeability of around 200 cc/(m²·day·atm) at 23°C, while a 2 mil LDPE is half that, at ~100. But an 8 mil EVOH film is like 0.1 cc/(m²·day·atm)—that’s basically airtight, which is why it’s used for long shelf-life foods.

Then there’s processing—how we make the film matters a ton too. Two films made of the exact same polymer can have totally different permeability if they’re processed differently. Like, if you stretch a film during manufacturing (we call that orientation), you can align the polymer chains to be more ordered, which makes the barrier better. Biaxially oriented polypropylene (BOPP) is a perfect example—regular PP is pretty permeable, but when you stretch it in two directions, the chains line up tight, so it’s way better at blocking oxygen and water vapor. We use BOPP for a lot of snack packaging, like candy bars or granola bars, because it’s lightweight, cheap, and has a solid barrier. Also, additives—stuff like plasticizers or fillers can change permeability. Plasticizers make the polymer chains more flexible, which lets gases slip through easier, while fillers like clay can act like little roadblocks, making the barrier better. That’s why we’re careful with additives—too much of one and you ruin the barrier you worked hard to get.

Wait, let’s talk about real-world applications, because that’s what everyone cares about. I’ve seen so many clients buy a film that looks good on paper, but fails in actual use because they didn’t match the permeability to their product. Let’s break down a few common uses:

Fresh produce: Berries, apples, leafy greens. These are living things, right? They breathe, so they take in oxygen and release carbon dioxide. If you use a film that’s too impermeable, the CO2 builds up inside the bag, and the produce rots. If it’s too permeable, the oxygen escapes too fast, and they wilt. That’s why we use perforated films or films tuned to let just the right amount of gases pass—we call that “respiratory-modified packaging.” For example, a bag for strawberries needs a little higher permeability than a bag for apples, because strawberries breathe faster. I remember a client last year who was using a regular LDPE bag for their organic spinach, and it was going bad in 2 days. We switched them to a custom-perforated PE film with permeability calibrated for leafy greens, and suddenly their spinach was lasting 5 days in the store—no more waste, no more returns. That’s the stuff that makes my job worth it.
Packaged food: Chips, nuts, jerky. These products don’t breathe, so they need to block oxygen to prevent staleness and spoilage. That’s why we use films with high oxygen barrier—usually laminated films with EVOH or PA (polyamide, also called nylon). For example, a potato chip bag is usually a 3-layer film: PE (inside, seals to the chip), aluminum foil (blocks light and gases), and PET (outside, protects the foil). The foil makes it almost totally impermeable, so chips stay crispy for months. But if foil is too expensive or you need a flexible film, we use high-barrier EVOH laminates that don’t have foil—those are great for snacks that need to avoid aluminum for dietary reasons.
Medical/pharmaceutical stuff: This is where permeability is non-negotiable, almost. For things like blister packs for pills, you need a film that blocks oxygen and moisture totally, because even a tiny bit of moisture can make pills break down. For sterile wound dressings, you need a film that lets water vapor (sweat) pass through, but blocks bacteria and oxygen, so the wound stays moist and doesn’t get infected. I can’t stress enough how critical this is in medical use—one wrong film and you’ve got a product that’s unsafe, which is why we only work with films that meet FDA and ISO standards for medical applications.
Industrial uses: Things like shrink wrap for pallets, or films for protecting electronic parts. For shrink wrap, you need a film that’s permeable enough to let air escape when you heat it, so it tightens around the pallet evenly. For electronic parts, you need a film that blocks moisture, because even a tiny bit of humidity can ruin circuit boards. I’ve had a tech client who was using the wrong film for their circuit board packaging, and they had 10% of parts get damaged during shipping because the film let moisture in. We switched them to a moisture-barrier polyolefin film, and that problem went away.

Now, let’s get into how we test permeability—this is another big one clients ask about, because numbers matter. There are standard tests, right? For oxygen permeability, we use ASTM D3985, which measures how much oxygen passes through a film over a certain time, area, and pressure. For water vapor, it’s ASTM E96. The units are usually cc/(m²·day·atm) for oxygen, or g/(m²·day) for water vapor. When a client comes to me with a specific need, I first ask: what product are you packaging? What’s the shelf life you need? What are the storage conditions (temperature, humidity)? Then I run tests on sample films to match exactly what they need. It’s not one-size-fits-all, that’s for sure.

Here’s some common myths I hear all the time, let’s bust those. First myth: “Thicker film is always better barrier.” No, like I said earlier—if you double the thickness, you halve permeance, but sometimes you can get a better barrier by switching to a different polymer. For example, 2 mil EVOH is way better barrier than 10 mil LDPE, and way thinner and more flexible. So thickness isn’t the only factor. Second myth: “All barrier films are the same.” Nope—EVOH, PA, PVDC, aluminum foil, each has their own pros and cons. EVOH is great for oxygen, bad for moisture; PVDC is moisture-resistant but has some environmental concerns; foil is super barrier but can be heavy and not recyclable. We work with clients to pick the best one for their needs, not just the most expensive. Third myth: “Permeability is only about gases.” Water vapor permeability is a huge part of it too—sometimes called moisture vapor transmission rate (MVTR). For example, a bag for bread needs to let a little moisture escape so it doesn’t get soggy, but block oxygen so it doesn’t go stale. That’s balancing gas and water vapor permeability, which is a fine line.

As a supplier, I get that a lot of clients don’t have a background in polymer science, so it’s my job to walk through all this without making them feel lost. I don’t just sell a film and move on—we work with them from the start, testing samples, adjusting formulations, making sure the film fits their exact use case. I’ve been doing this long enough to know that a good film isn’t just about the specs on a sheet—it’s about solving their specific problem. Last year, a craft brewery came to me looking for a film to package their canned craft beer. They didn’t want aluminum cans because they were heavy, and they needed the beer to stay fresh for 6 months. We worked together to create a custom laminated film with a high-barrier EVOH layer, and we did tests to make sure it blocked oxygen enough, and also let just a tiny bit of CO2 escape so the beer didn’t go fizzy in the wrong way. It took a couple of rounds of samples, but it worked, and they’ve been a regular client ever since. That’s the kind of relationship I value more than anything.

Now, if you’re here because you’re looking for a plastic film for your product—whether it’s food, medical, industrial, whatever—here’s what you should think about before reaching out. First, know your end goal: is it to keep oxygen out? Moisture in? Let gases escape? How long does your product need to last? What’s the storage environment (hot, cold, humid, dry)? How important is flexibility vs. strength? Once you have those answers, that’s half the battle. And if you don’t know the answers, that’s okay too—we’re here to help.

Wait, let’s wrap this up. Gas permeability of plastic film isn’t just some tech buzzword—it’s the reason the products we use every day work as well as they do. It’s a balance of polymer type, thickness, processing, and testing, and getting that balance right can make or break a product’s shelf life, safety, and success. As a plastic film supplier, my job isn’t just to sell you a roll of film—it’s to help you pick the right one for your specific needs, no jargon, no guesswork.

If you’re working on a project and need a film with the right gas permeability, or you have questions about anything we talked about today, don’t hesitate to reach out. We can send free samples, run tests, walk through all the options, whatever you need. Let’s make your product work as well as it can.

Mailing Bags 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
Paul, D. R., & Yampolskii, Y. P. (1994). Polymeric Gas Separation Membranes. CRC Press.
Robertson, G. L. (2013). Food Packaging: Principles and Practice (3rd ed.). CRC Press.

Xiamen Leadkit Group Co., Ltd.
Xiamen Leadkit Group Co., Ltd. is one of the most professional plastic film manufacturers and suppliers in China, specialized in providing high quality customized service. Please feel free to wholesale cheap plastic film from our factory. Contact us for more details.
Address: No.398, Jiahe Road, Huli District, Xiamen, Fujian, China
E-mail: effie@leadkitpackaging.com
WebSite: https://www.leadkitpackaging.com/