As a Thermoplastic Urethane (TPU) film supplier, the question I get asked most often isn’t about tensile strength, scratch resistance, or cost—it’s about oxygen transmission rate (OTR). That makes total sense, right? OTR isn’t just a random technical spec; it’s the make-or-break performance metric for so many of our customers’ end products, from medical packaging to outdoor inflatables to sports gear. Too much oxygen seeping through a TPU film, and a food packaging bag might spoil before it even hits the shelf, a medical device’s sterile barrier could fail, or a hiking boot’s waterproof lining might let in moisture that ruins the wearer’s day. After 12 years working directly with TPU film formulation and customer applications, I’ve learned that explaining OTR to someone who doesn’t work in polymer chemistry isn’t just about throwing numbers around—it’s about connecting that number to what they actually need their product to do. Let’s break this down, no stuffy jargon, just real talk from someone who tests OTR on our production floor every single week. Thermoplastic Urethane Film
First, let’s get one basic truth out of the way: TPU isn’t a single material. That’s the biggest mistake I see customers make when they ask about OTR—they think all TPU films have the same OTR, like all plastic water bottles hold the same amount of liquid. Nothing could be further from reality. TPU is a block copolymer, made of hard segments and soft segments, and tweaking the ratio, type, or molecular weight of those segments changes every single property—including OTR. For example, a TPU formulation with a high percentage of soft, flexible polyether segments will have a much higher OTR than a TPU loaded with rigid aromatic hard segments. Why? Think of it like a sponge: soft segments are more flexible and let small gas molecules slip through easier, while hard segments create a tighter, more packed structure that acts as a barrier. That’s why when a customer comes to us and says “I need a TPU film with low OTR for oxygen-sensitive pharmaceuticals,” our first step isn’t to quote a random spec—it’s to ask three key questions: how thick does their film need to be, what’s their desired shelf life, and what temperature and humidity conditions will their product be in?
Thickness is the single biggest factor that affects OTR, and it’s way simpler than most people realize. The standard way to measure OTR is in cm³ per square meter per 24 hours, at a specific temperature and humidity—usually 23°C and 0% relative humidity, per ASTM D3988, the most widely used test method for flexible barrier films. The key here is that OTR is inversely proportional to thickness. That means if you double the thickness of a TPU film, you cut its OTR in half. Let’s use real numbers from our own production to make this concrete. Our standard food-grade polyether TPU film, for example, has an OTR of roughly 80 cm³/(m²·24h) when it’s 25 microns thick. If that customer needs a tighter barrier, we can make a 50-micron thick film, and its OTR drops to 40 cm³/(m²·24h)—exactly half. If they need even better, a 100-micron thick TPU film from that same formulation will have an OTR of 20 cm³/(m²·24h). That’s not magic; it’s just basic diffusion. Gas molecules move through tiny gaps in the polymer structure, so the thicker the film, the longer those gaps have to be, and the harder it is for oxygen to travel all the way through.
But thickness isn’t the only variable—polymer chemistry plays an even bigger role, especially when customers need ultra-low OTR. Polyester-based TPUs, for example, naturally have lower OTR than polyether-based TPUs. Why? Polyester segments are more polar, which creates stronger intermolecular bonds between polymer chains, closing up those tiny gaps that oxygen uses to move through. Let’s compare: a 25-micron polyester TPU film from our line has an OTR of around 45 cm³/(m²·24h), almost half that of our polyether TPU. If we add specialty additives—like nano-clays or barrier coatings—we can push that even lower. For our medical-grade grade barrier TPU, we engineered a formulation with a blend of polyester and hard aliphatic segments, plus a proprietary cross-linking process, that gives a 25-micron film an OTR of just 18 cm³/(m²·24h). That’s the spec we use for sterile packaging for single-use surgical tools, where even a tiny amount of oxygen over a 2-year shelf life would break down the product’s packaging integrity.
Now, I’ve had more than a few customers call me and say, “I saw a TPU film online with an OTR of 5 cm³/(m²·24h)—can you match that?” and I have to pause and ask a few follow-up questions. First, is that measurement at the standard test conditions (23°C, 0% RH)? Because OTR skyrockets with temperature. Leave a TPU film on a hot loading dock in the summer, and its OTR can double or even triple. Humidity also matters, especially for polyether TPUs, which absorb moisture. Water molecules take up space in the polymer structure and weaken intermolecular bonds, making it easier for oxygen to pass through. For example, our standard polyether TPU’s OTR jumps from 80 to 150 cm³/(m²·24h) when tested at 50% RH—something no vendor will tell you if they only cite dry OTR numbers. That’s why testing at conditions that match the customer’s actual end use is non-negotiable. We test every batch of our TPU film at both 0% and 50% RH, and for medical and food customers, we also offer custom testing at their specific temperature and humidity ranges. I once worked with a customer making frozen food packaging that would sit in a -18°C freezer for 12 months; their OTR at standard conditions was fine, but at -18°C, our TPU’s OTR dropped to less than 10 cm³/(m²·24h), which was perfect for their need to keep frozen meats fresh without freezer burn.
Another common misconception I run into is that lower OTR is always better. That’s not true, either. For some applications, you actually need a higher OTR. For example, a breathable wound dressing needs to let oxygen pass through to the wound to promote healing—so a TPU film with an OTR of 1,000 cm³/(m²·24h) might be exactly what that customer needs. Or for some flexible electronics, where you need vapor transmission along with gas permeability, a higher OTR is a feature, not a bug. That’s why our job isn’t to sell customers the lowest OTR TPU film; it’s to find the right OTR for their specific application. We had a customer last year making inflatable stand-up paddleboards (SUPs) who initially asked for the lowest OTR film we had. After talking through their needs, we realized they wanted a durable, flexible TPU that would hold air, but they didn’t need a super-tight barrier—they were more concerned with abrasion resistance and UV stability. The low OTR barrier film we quoted them would have cost 30% more than their needs required, and been unnecessarily stiff, making the SUP hard to fold and store. We swapped it for our standard flexible TPU film, which had an OTR of 120 cm³/(m²·24h) at 25 microns, and that worked perfectly for their needs. It held air for months, was flexible enough to fold into a car trunk, and was half the cost of the barrier film they initially asked for. That’s the value of working with a supplier who actually listens, not just quotes specs.
Now, you might be wondering, how do we measure OTR accurately? That’s a question I get all the time, and it’s not just for our internal testing—customers often ask to see our test data for each batch. We use a Mocon OX-TRAN instrument, which is the industry standard for OTR testing. The instrument uses a coulometric sensor to measure the amount of oxygen that passes through a sample of TPU film over a 24-hour period, at controlled temperature and humidity. Every batch of our TPU film, whether it’s 10 microns thick for a stretchable glove or 200 microns thick for a heavy-duty inflatable, is tested three times, and we include the test certificates with every order. No surprises, no hidden numbers, just transparent data that our customers can use for their own regulatory and quality audits. For medical-grade TPU, we also perform additional testing per ISO 10993 standards, which means our OTR data is accepted by regulatory bodies like the FDA and CE for use in medical devices.
I’ve seen first-hand what happens when OTR is miscalculated. A few years ago, we had a customer who made pet food packaging decide to switch to a cheaper TPU film from another supplier. They quoted us a film with an OTR of 70 cm³/(m²·24h) for their 25-micron film, which they thought was fine for a 6-month shelf life. But they didn’t account for the fact that their packaging would sit on store shelves at 30°C and 70% RH for months. The actual OTR of that competitor’s film at their storage conditions was over 200 cm³/(m²·24h), which was way too high. By the time the pet food hit store shelves, the oxygen had oxidized the fats in the food, making it go rancid. They had to recall 50,000 units, which cost them hundreds of thousands of dollars, and switch back to our TPU film after that. That’s why we always emphasize to new customers that OTR isn’t just a number on a spec sheet—it’s a functional performance property that needs to be matched to their end use, temperature, humidity, and shelf life.
So, to wrap this up, what is the oxygen transmission rate of TPU film? The answer is, it depends. It depends on the TPU’s polymer chemistry (polyether vs. polyester vs. specialty blends), its thickness, the testing conditions (temperature, humidity), and the additives used in the formulation. As a TPU film supplier with 12 years of in-house testing and application expertise, we don’t just offer one OTR value—we offer a range of custom-formulated TPU films with OTR specs from less than 10 cm³/(m²·24h) for sterile medical packaging, up to over 2,000 cm³/(m²·24h) for breathable wound care and flexible electronics. The key is knowing what you need, not just what’s the lowest or highest number. If you’re a packaging engineer, a medical device designer, a sports gear manufacturer, or anyone working with TPU film, OTR is a critical spec to get right. Don’t rely on generic spec sheets—talk to a supplier who will work with you to test, adjust, and deliver a TPU film that meets your exact needs. We’ve spent years refining our formulations, testing processes, and customer support to make that happen, and we’re always here to walk through OTR specs, custom formulations, or batch test data whenever you need. Reach out to our team to discuss your application, and we’ll help you find the right TPU film for your project.
TPU Hot Melt Adhesive Film References
- ASTM D3988, Standard Test Method for Water Vapor Transmission Rate of Flexible Barrier Materials
- ISO 10993, Biological Evaluation of Medical Devices
- Seymour, R. B., & Carraher, C. E. (2001). Polymer Chemistry: An Introduction (4th ed.). Marcel Dekker.
- Mocon Inc. (2022). Oxtran OTR Testing for Flexible Packaging Applications. Technical Note.
Suzhou Xinqipu New Materials Technology Co., Ltd.
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