As a Thermoplastic Polyurethane (TPU) film supplier, I get this question at least twice a week from engineers, product designers, and procurement teams looking to spec the right material for their applications: “What’s the coefficient of friction (COF) of TPU film?” It’s easy to treat COF as a random, one-time number, but over years of working with TPU films for uses ranging from automotive interior liners to medical device packaging, I’ve learned that COF isn’t a static value—it’s a performance metric that shifts based on how the film is made, treated, and used. Let’s break this down, from what COF actually means for TPU film, to what numbers you can expect, to how our team adjusts it to fit your exact needs. Thermoplastic Polyurethane Film
First, a quick refresher for anyone new to COF: Coefficient of friction is a dimensionless number that measures the resistance between two surfaces when they move (or try to move) against each other. There are two key types: static COF, which is the force needed to start movement between two surfaces, and kinetic COF, which is the force needed to keep that movement going. For TPU film, both numbers matter a lot because they directly impact how easy a product is to handle, process, and use down the line. For example, a TPU film used for stretch wrap on pallets needs a low COF to slide easily over stacks of goods during packaging, while a TPU film used for a medical device drape needs a high COF to stay in place on a patient’s skin without slipping.
When it comes to TPU film specifically, the base COF isn’t a one-size-fits-all. Let’s start with our standard, unmodified TPU film—what we call our general-purpose grade. For this film, tested per ASTM D1894, the standard test method for plastic film and sheeting, the static COF ranges from 0.6 to 0.8, and kinetic COF ranges from 0.5 to 0.7. That’s for the film’s smooth, untreated surface, tested against a common substrate: stainless steel, which is the industry standard for these tests, and also the surface you’ll most often see TPU films sliding against during processing, like on conveyor belts or machinery rollers. But here’s the catch: that base number is just a starting point. TPU’s chemical makeup, manufacturing process, and any post-production treatments can shift this number dramatically, and that’s where our expertise as a TPU film supplier comes in.
TPU is a versatile polymer, made from soft polyether or polyester segments and hard urethane segments. The ratio of these segments directly impacts COF. Polyether-based TPU, which is our most popular grade for durable, flexible applications, naturally has a lower surface energy than polyester-based TPU. Lower surface energy means less adhesion between surfaces, so polyether TPU’s base COF is typically 0.1 to 0.2 lower than polyester TPU. For example, our polyether general-purpose TPU films have a kinetic COF of 0.5 to 0.6, while our polyester grades come in at 0.6 to 0.7. That difference might seem small on paper, but it makes a huge difference during high-speed manufacturing lines. A customer making athletic shoe uppers told us last year that switching from a polyester TPU to our polyether grade cut the film’s static COF enough that they could run their stamping presses 15% faster, reducing downtime and speeding up their production by nearly a full shift a week.
Another big factor in TPU film COF is the film’s thickness. Thinner films, typically 1 mil (0.001 inches) to 5 mils, have a higher surface area-to-volume ratio, so any inherent surface roughness or additives have a more pronounced effect on COF. Our 1 mil polyether TPU film, for example, has a static COF of 0.65, while our 10 mil thick polyether TPU film has a static COF of 0.55—same base polymer, same test conditions, just a thicker film with fewer surface irregularities. For our customers making packaging for small electronics, where they need thin, flexible TPU film that slides easily into blister packs, that 0.1 difference is the gap between a film that feeds smoothly through automatic packaging machines and one that jams every 10 minutes.
Now, the parts of COF that most people don’t consider: environmental factors and how the film is treated after manufacturing. TPU is hygroscopic, meaning it absorbs moisture from the air. High humidity can increase TPU’s surface adhesion, raising COF by 0.1 to 0.3. We had a customer making food packaging for frozen fish who ran into this last winter: they sourced TPU film from a different supplier, and when humidity hit 80% in their warehouse, the film’s COF jumped to 0.9, high enough that the packaging rolls would stick together on their inventory shelves. Our team worked with them to modify the film with a slip additive that resists moisture absorption, bringing their COF back down to 0.6 even in high humidity, and they’ve been using our film ever since. That’s the kind of real-world problem solving you can’t get from a generic COF number on a spec sheet.
Post-production surface treatments are the biggest tool we use to adjust TPU film COF for specific applications. If a customer needs a low COF for slip, we can add permanent slip agents—usually erucamide or oleamide, which are common, non-migratory additives that bloom to the film’s surface over time. For our low-slip TPU films, we can get static COF as low as 0.12 and kinetic COF as low as 0.1, which is used for things like conveyor belting liners or pallet wrap. On the other end, if a customer needs a high COF to prevent slipping, like for medical drapes, shoe soles, or grip strips, we can modify the film’s surface to add texture, or add anti-slip additives that increase surface adhesion. Our high-slip TPU films have a static COF of 1.2 to 1.8, tested against skin or fabric, which is perfect for products that need to stay in place without adhesive.
There’s a common myth among new product designers that all low-COF TPU film is the same, but that’s not true. Some slip agents are temporary—they wear off after a few uses or when the film is exposed to harsh chemicals, which is a big problem for outdoor applications like vinyl wraps or marine covers. At our facility, we use permanent, non-migratory slip agents that stay effective for the full lifecycle of the film, even when exposed to UV light, cleaning chemicals, or extreme temperatures. A customer making marine seat covers tested a competitor’s low-slip TPU film, and after 6 months of exposure to saltwater and sun, their film’s COF jumped back up to 0.8, causing the seats to slip when the boat hit waves. They switched to our UV-stabilized TPU film, and their COF has stayed at 0.3 for over 2 years now. That’s the difference between a COF number that works in a lab and one that works in the real world.
I also want to address how test methods can skew COF numbers, because that’s another common point of confusion. The standard is ASTM D1894, but some suppliers test COF against different substrates, not stainless steel. If a supplier tests their TPU film against rubber instead of stainless steel, they’ll get a much higher COF number, because rubber has higher surface adhesion. If a customer is spec’ing COF for their application, it’s critical to ask what substrate the test uses. For example, if you’re using TPU film on a rubber conveyor belt, our COF numbers tested against rubber will be different than those tested against stainless steel—we can run tests with your exact processing substrate to give you a number that’s accurate for your line, not just the standard test.
Another question we get: how does TPU’s COF change when it’s bonded to other materials, like fabric or adhesive? For laminating TPU film to polyester fabric, the COF of the final laminate will be a mix of the TPU’s surface and the fabric’s texture. If you’re laminating TPU to a soft, smooth fabric, the COF will be close to the TPU’s base number, but if you’re laminating to a textured, woven fabric, the COF will be higher, as the fabric creates more surface roughness. We work with laminators to test both the film’s COF and the final laminate’s COF to make sure it fits your needs—for a luggage outer shell, a slightly higher COF is good for grip, but for a backpack lining, a lower COF makes the backpack easier to slide over other bags in storage.
Let’s also talk about what COF means for processing, because that’s where most of our customers feel the impact the most. When you’re running 1,000 feet of film per minute on an automatic line, a COF that’s too high can cause wrinkles, jams, or tears. A COF that’s too low can cause the film to slip too much on rollers, leading to misalignment or uneven cutting. Our production team works closely with each customer to nail down the exact COF they need before we even start production. Last year, a customer making disposable face shields came to us with a problem: their existing TPU film was too low in COF, so the clear film would slip off the headband mid-assembly, and too high, so it would jam on the cutting die. We tested their exact line’s rollers and headband material, adjusted the film’s slip additive to get a static COF of 0.45—right in the middle of their range—and that cut their assembly error rate from 8% to less than 1% overnight. That’s the kind of value that comes from understanding COF as more than just a number, but a tool to make your production run smoother and your final product better.
If you’re currently sourcing TPU film, you’ve probably noticed that COF numbers are inconsistent across suppliers. One supplier might say their TPU has a COF of 0.3, another says 0.7, and neither is lying—they just tested it under different conditions, with different additives, or for different substrates. As a TPU film supplier, we don’t just send you a generic spec sheet. We ask about your application: are you running the film on stainless steel rollers or rubber? Do you need it to grip skin for medical use, or slide over pallets for shipping? Does it need to work in high humidity or extreme heat? All of these questions go into determining the right COF for your product.
Now, if you’re gearing up for a new product launch, troubleshooting a processing issue, or looking to switch TPU film suppliers for better COF control, we’re here to help. Our team has decades of experience working with TPU film for every industry—automotive, medical, packaging, sports and recreation, and more—and we can test your existing film’s COF, adjust it to meet your specs, or even develop a custom TPU film with exactly the right COF for your needs. We don’t believe in one-size-fits-all materials, and that includes COF. Whether you need a low-slip film that moves smoothly through your line, or a high-slip film that stays firmly in place, we can deliver it.
Don’t waste time troubleshooting with inconsistent COF numbers from suppliers who don’t understand your application. Reach out to our team to discuss your TPU film needs, and we’ll work with you to find the perfect COF, along with all other performance specs, for your project.
Thermoplastic Urethane Film References:
- ASTM International. (2021). Standard Test Method for Static and Kinetic Coefficients of Friction of Plastic Film and Sheeting (ASTM D1894-21). West Conshohocken, PA: ASTM International.
- Petrovic, Z. S. (2000). Thermoplastic polyurethanes: properties and applications. Progress in Polymer Science, 25(5), 697-725.
- Zhang, L., et al. (2018). Surface modification of thermoplastic polyurethane films for controlled coefficient of friction. Journal of Applied Polymer Science, 135(22), 46278.
Suzhou Xinqipu New Materials Technology Co., Ltd.
As one of the most professional thermoplastic polyurethane film manufacturers and suppliers in China, we have world-leading production equipment and strong manufacturing capabilities. Please feel free to wholesale bulk customized thermoplastic polyurethane film from our factory. Also, quotation is available.
Address: No.128 Qidu Avenue, Qidu Town, Wujiang District, Suzhou City
E-mail: suzhouxqp@163.com
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