{"id":3494,"date":"2026-09-29T02:58:20","date_gmt":"2026-09-28T18:58:20","guid":{"rendered":"http:\/\/www.nuecesdealgodon.com\/blog\/?p=3494"},"modified":"2026-09-29T02:58:20","modified_gmt":"2026-09-28T18:58:20","slug":"how-to-test-the-thermal-conductivity-of-polyimide-4804-ce400c","status":"publish","type":"post","link":"http:\/\/www.nuecesdealgodon.com\/blog\/2026\/09\/29\/how-to-test-the-thermal-conductivity-of-polyimide-4804-ce400c\/","title":{"rendered":"How to test the thermal conductivity of polyimide?"},"content":{"rendered":"

If you\u2019ve ever worked with polyimide (PI) materials\u2014whether as an engineer designing high-temperature electronics, a technician assembling aerospace components, or a quality control specialist checking material consistency\u2014you know thermal conductivity is non-negotiable. PI is our core product as a polyimide supplier, and for years, we\u2019ve heard from clients that they struggle to test this property accurately. Too often, tests are rushed, methods are mismatched, or results are misinterpreted, leading to poor part performance or overspending on unnecessary material tweaks. Today, I want to break down how to test the thermal conductivity of polyimide correctly, straight from the perspective of a supplier that\u2019s tested our own materials and helped hundreds of clients get reliable data. No jargon for jargon\u2019s sake, just practical, science-backed steps that work for PI, a material that\u2019s uniquely tricky to test compared to metals or even other polymers. Polyimide<\/a><\/p>\n

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First, let\u2019s ground this in why PI\u2019s thermal conductivity matters, because it\u2019s not just a random material property. PI is used in everything from flexible printed circuits (FPCs) that wrap around smartphone cameras to insulation for jet engine wiring and thermal barriers in electric vehicle batteries. For these applications, if heat can\u2019t move through the PI consistently, you get hot spots\u2014frayed wiring, failed circuits, or even battery thermal runaway risks. That\u2019s why testing isn\u2019t a box-ticking exercise for our team here; it\u2019s how we ensure the PI we supply meets your needs, and how we help you verify that the PI you\u2019re using actually performs as specified.<\/p>\n

Now, let\u2019s get to the testing part, starting with the most critical pre-test step: sample preparation. Most people skip this, and it\u2019s the #1 reason test results are wrong for PI. PI can be in three main forms: film, molded parts, or coated layers, and each needs a different approach. For thin PI films (our most common product, 12.5\u03bcm to 250\u03bcm thick), you can\u2019t just grab a random scrap from a roll. You need at least three identical samples, each 10mm x 10mm in size, cut parallel to the machine direction (MD) and cross direction (CD) of the roll\u2014PI is anisotropic, meaning thermal conductivity is different along vs. across the direction the film was stretched during manufacturing. Skip the direction step, and your MD result could be 30% higher than your CD result, leading to confusion about which value to use for design. For molded PI parts (used in structural components), you\u2019ll need thicker samples, 3mm to 5mm thick, with flat, parallel surfaces\u2014no rough edges from machining, because gaps or uneven surfaces will skew test readings. For coated PI layers (like on silicon wafers), the sample has to stay on the wafer, and you\u2019ll need a reference wafer of known thermal conductivity to subtract the substrate\u2019s contribution.<\/p>\n

Next, choosing the right test method. This is where most people go wrong\u2014using a method meant for metals on PI, which is a thermal insulator, not a conductor. There are three primary methods for PI, and each is suited to a specific use case. Let\u2019s walk through them, with notes on when to use each, and what pitfalls to avoid.<\/p>\n

The first and most common method for thin PI films (like FPC substrates) is the Laser Flash Analysis (LFA). Here\u2019s how it works: you place your sample in a machine that heats one side with a tiny laser pulse, then measures how fast the heat travels to the opposite side with an infrared detector. The time it takes for heat to cross the sample (called the \u201chalf-time\u201d) is used to calculate thermal diffusivity, and then thermal conductivity is calculated using the formula: k = \u03b1 * \u03c1 * Cp, where \u03b1 is diffusivity, \u03c1 is density, and Cp is specific heat capacity. For PI, you have to be careful with the temperature here\u2014most LFA machines run at room temp, but if you need thermal conductivity at operating temperatures (like 150\u00b0C for EV applications), you\u2019ll need a high-temperature LFA. Also, you need to coat the sample with a thin layer of graphite or gold to absorb the laser pulse\u2014PI is translucent, so a bare sample would let the laser pass through instead of heating the surface. We\u2019ve seen clients skip this coating step and get diffusivity values 2x lower than they should, which makes their PI seem less thermally efficient than it is.<\/p>\n

The second method is the guarded hot plate (GHP), which is better for bulk molded PI parts or thick films. GHP works by sandwiching the sample between two heated plates, measuring the heat flow that passes through the sample when it\u2019s at a steady temperature. This method is more accurate for absolute thermal conductivity values, because it accounts for heat loss from the edges of the sample (the \u201cguarded\u201d part uses a ring around the plates to prevent that). The downside is that GHP needs samples at least 5mm thick, so it\u2019s not ideal for thin PI films. We use GHP for testing our molded PI components because it gives us data that\u2019s perfect for structural design in aerospace and automotive parts, where thermal stability is critical. One tip for GHP: make sure the sample is completely free of voids. PI can trap small air bubbles during molding, and those voids will act as thermal barriers, lowering your k value by 10-15%. Always inspect samples with a microscope before testing, and discard any with visible defects.<\/p>\n

The third method is the transient plane source (TPS) method, also called the hot disk method. This is great for small samples or coated layers, like PI on semiconductors. The TPS uses a thin, nickel sensor sandwiched between two halves of your sample (or between the PI layer and a reference substrate). The sensor heats up slightly, and measures its own resistance change, which lets you calculate thermal conductivity in real time. The biggest advantage here is that you don\u2019t need to calculate diffusivity and Cp separately\u2014though you do need to input the correct Cp value for your PI grade, which is why using our material specs here is important. If you use the wrong Cp, your k value will be off by up to 8%.<\/p>\n

Now, a common question we get: what results should I expect for polyimide? As a supplier, we make several grades of PI, and their thermal conductivity ranges from 0.12 W\/mK for standard unfilled PI to 0.8 W\/mK for thermally filled PI (filled with boron nitride or aluminum oxide particles). Standard PI is an electrical insulator, so its thermal conductivity is low\u2014think of it as a thermal barrier, which is what makes it great for high-temperature insulation. But if you need PI that moves heat, like in LED heat sinks, you\u2019ll want our thermally filled grades, which use our proprietary particle dispersion process to avoid clumping, so the heat flows evenly without sacrificing PI\u2019s chemical resistance. If your test comes back lower than our spec, don\u2019t panic\u2014first check your sample preparation: did you test MD vs CD? Did you coat LFA samples? Did you account for voids? We\u2019ve had clients send us test results that were 20% lower than our spec, turn out to have used a sample with a scratch that created a tiny air gap, skewing the GHP reading.<\/p>\n

Another key point: testing at operating temperature, not just room temperature. Most material data sheets list thermal conductivity at 25\u00b0C, but PI\u2019s k value changes with temperature. For example, standard unfilled PI\u2019s thermal conductivity stays roughly constant up to 200\u00b0C, then decreases slightly as the polymer chains soften. Filled PI might increase slightly as the filler particles conduct more heat at higher temps, because the polymer matrix becomes more flexible and the particles are able to connect more. If your application is at 125\u00b0C inside an EV battery, testing at room temp won\u2019t give you usable data\u2014you\u2019ll need a method that can run at your operating temp, which is why our in-house testing lab has LFA machines that go up to 500\u00b0C, so we can provide temperature-corrected data for every grade we supply.<\/p>\n

Let\u2019s talk about common mistakes we see all the time, to save you the headache. First, using the wrong sample size for thin films: if your PI film is 25\u03bcm thick, you can\u2019t use GHP, because the heat will conduct through the plates\u2019 interfaces instead of the sample. Stick to LFA or TPS for thin films. Second, mixing up anisotropy: as I mentioned earlier, PI\u2019s thermal conductivity is directional. If you\u2019re designing a flexible FPC that will bend along the MD, you need the MD k value, not the average of MD and CD. If you test both, you\u2019ll get a range, so you need to know what direction is relevant for your part. Third, not calibrating your equipment. Every thermal test machine needs calibration with a reference material of known k value\u2014like a quartz standard or a copper sample. We calibrate our in-house machines monthly, and we always advise clients to do the same, especially if they\u2019re getting data used for design or compliance.<\/p>\n

If you\u2019re testing PI for a new project, here\u2019s a quick step-by-step guide to follow, tailored to our experience:<\/p>\n

    \n
  1. Define your application: is it thin film, bulk molded, or coated on a substrate? What\u2019s your operating temperature range?<\/li>\n
  2. Source three identical samples, cut to the correct size and orientation (MD\/CD for films) for your chosen test method.<\/li>\n
  3. Inspect samples for voids, scratches, or defects\u2014discard any that are not perfect.<\/li>\n
  4. Choose a calibrated test method: LFA for thin films at temps up to 500\u00b0C, GHP for bulk parts, TPS for small\/coated samples.<\/li>\n
  5. Input the correct Cp value for your specific PI grade (we provide these free to all our clients, just reach out).<\/li>\n
  6. Run three tests per sample, average the results, and compare to our grade specs\u2014don\u2019t rely on a single test result, because small variations can happen at the micro level.<\/li>\n<\/ol>\n

    As a polyimide supplier, our goal isn\u2019t just to send you PI rolls or molded parts\u2014it\u2019s to make sure you have the data to use them correctly. If you\u2019ve tested PI and gotten results that don\u2019t align with what you expected, or if you need help choosing the right test method, or if you just want to confirm that our PI grades will work for your application, our technical team is here to walk through it with you. We\u2019ve spent 15 years refining our testing processes, and we\u2019ve helped thousands of engineers avoid costly mistakes from incorrect thermal conductivity data. Whether you\u2019re prototyping a new flexible circuit, designing aerospace wiring insulation, or building an EV battery thermal management system, thermal conductivity is make-or-break, and getting the test right is the first step to making your project a success.<\/p>\n

    <\/p>\n

    Don\u2019t settle for generic test data that doesn\u2019t account for PI\u2019s unique properties. Reach out to us to discuss your testing needs, or to get a custom sample of our PI grade with temperature-specific thermal conductivity data tailored to your operating conditions. We\u2019re here to partner with you, not just supply materials.<\/p>\n

    OLED Material<\/a> References<\/p>\n

      \n
    1. Turi, E. A. (Ed.). (1996). Polyimides: Fundamentals and Applications. CRC Press.<\/li>\n
    2. Zhang, Y., et al. (2018). Thermal conductivity of polyimide films: A review. Polymer Testing, 69, 371-382.<\/li>\n
    3. ASTM E1461-22, Standard Test Method for Thermal Diffusivity by the Flash Method. ASTM International.<\/li>\n
    4. ASTM D5470-17, Standard Test Method for Thermal Transmission Properties of Thermally Conductive Electrical Insulation Materials. ASTM International.<\/li>\n<\/ol>\n
      \n

      Hubei Jiutian Bio-medical Technology Co., Ltd.<\/a>
      Hubei Jiutian Bio-medical Technology Co., Ltd. is one of the most professional polyimide manufacturers and suppliers in China, also supports customized service with low price. Please feel free to buy bulk cheap polyimide made in China here from our factory. For free sample, contact us now.
      Address: Room 105, Building 1, Zhongchuang Tower, No. 2 Darui Road, Guandong Industrial Park, Wuhan East Lake High-Tech Development Zone
      E-mail: info@jiutian-bio.com
      WebSite:       https:\/\/www.jiutian-bio.com\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

      If you\u2019ve ever worked with polyimide (PI) materials\u2014whether as an engineer designing high-temperature electronics, a technician … How to test the thermal conductivity of polyimide?<\/span>Read more<\/a><\/p>\n","protected":false},"author":295,"featured_media":3494,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[3457],"class_list":["post-3494","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry","tag-polyimide-453b-ce78c1"],"_links":{"self":[{"href":"http:\/\/www.nuecesdealgodon.com\/blog\/wp-json\/wp\/v2\/posts\/3494","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.nuecesdealgodon.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.nuecesdealgodon.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.nuecesdealgodon.com\/blog\/wp-json\/wp\/v2\/users\/295"}],"replies":[{"embeddable":true,"href":"http:\/\/www.nuecesdealgodon.com\/blog\/wp-json\/wp\/v2\/comments?post=3494"}],"version-history":[{"count":0,"href":"http:\/\/www.nuecesdealgodon.com\/blog\/wp-json\/wp\/v2\/posts\/3494\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.nuecesdealgodon.com\/blog\/wp-json\/wp\/v2\/posts\/3494"}],"wp:attachment":[{"href":"http:\/\/www.nuecesdealgodon.com\/blog\/wp-json\/wp\/v2\/media?parent=3494"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.nuecesdealgodon.com\/blog\/wp-json\/wp\/v2\/categories?post=3494"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.nuecesdealgodon.com\/blog\/wp-json\/wp\/v2\/tags?post=3494"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}