As a supplier specializing in heat resistant plastic, I get this question every single week from product designers, mechanical engineers, and even small-batch manufacturers who’ve just run into their first heat-related part failure. It’s a problem I’ve watched evolve over 12 years in this space: not too long ago, designers would grab standard ABS or polycarbonate for high-temperature applications, only to have parts warp at 120°C, crack under thermal cycling, or leach chemicals when exposed to industrial heat. Now, more folks are reaching out asking how to actually design with the materials we make—materials engineered to hold up where regular plastics fold, without the cost or weight of metal alternatives. Let’s break this down, from material selection to prototyping to production, the way I walk through it with every client who picks up the phone. Heat Resistant Plastic
First, let’s start with the basics that most people miss when they’re rushing to pick a heat resistant plastic. Heat resistance isn’t a single number—it’s tied to what the part will actually experience. I can’t tell you how many times a designer will come to me saying, “I need a plastic that can handle 150°C,” and when we dig a little, their part is only exposed to peak temperatures of 135°C for 20 minutes at a time, with 24 hours at 80°C in between. Choosing a high-performance polyether ether ketone (PEEK) for that? That’s 3x the material cost and way more complex to machine than necessary. Instead, we often point them to modified polyphenylene sulfide (PPS) or glass-reinforced polyamide 6/6 (PA66), which have continuous use temperatures around 160°C, can handle short-term spikes up to 200°C, and cost half what PEEK does.
The key here is distinguishing between two critical metrics: glass transition temperature (Tg) and deflection temperature under load (DTUL). Tg is the temperature where a plastic shifts from a rigid, glassy state to a rubbery, flexible one—above Tg, the material loses its structural integrity. DTUL, on the other hand, is the temperature at which a 1/8-inch thick test sample deflects 0.25% under a specific load, usually 1.8 MPa or 0.45 MPa. For load-bearing parts—think a gear for an industrial pump or a bracket for a automotive engine sensor—DTUL is way more important than Tg. A part that’s holding up 5 kg at 120°C needs to be rated for a DTUL that’s 20-30°C higher than its maximum operating temperature, not just its Tg. I always warn clients: if you’re designing a part that’s under stress at high heat, never size it right at the Tg or DTUL. Build in a 25-30°C buffer. That’s the difference between a part that lasts 6 months and one that runs for 10 years.
Next, material form matters just as much as the base polymer. Most heat resistant plastics come in four forms for end use: neat resin, glass-filled, mineral-filled, and carbon-fiber reinforced. Let’s be honest: neat PPS is soft and a little stretchy—great for gaskets, terrible for structural parts. Add 30% glass fiber, and suddenly that PPS has a tensile strength three times higher, a DTUL jump from 100°C to 160°C, and won’t warp when molded. But glass-filled materials have a catch: their shrinkage rate is uneven, so thin walls or complex geometries can cause warpage during injection molding. Carbon-fiber filled, meanwhile, is stiffer, has better dimensional stability, and even adds some electrical conductivity, but it’s more abrasive on mold tools—something a lot of new designers forget when they switch to carbon-fiber heat resistant plastic. I had a client last year who went all in on a carbon-fiber reinforced PA66 for a motorcycle intake manifold, only to have their mold tool wear out after 2,000 parts, because they didn’t account for the higher abrasion of carbon fiber. We ended up adjusting their mold steel and running a slightly lower fiber load, and they’ve been running at 10,000 parts a month ever since.
Then there’s the design geometry itself—this is where so many designers overcomplicate things, especially when switching from metal to heat resistant plastic. Metal can handle sharp corners and thin walls because it’s strong in compression and tension, but plastics, especially heat resistant ones, are much more prone to stress concentrations at sharp angles. I tell every client: round every internal and external corner with a radius equal to at least 10% of the wall thickness. If your wall is 3mm thick, a 0.3mm radius minimum, no exceptions. That small change reduces stress at the corner by 40% in finite element analysis (FEA) tests I’ve run with our engineering team, and it almost eliminates cracking during thermal cycling.
Wall thickness is another big one. Heat resistant plastics have lower thermal conductivity than metals—about 0.2 W/mK for PPS, compared to 43 W/mK for aluminum. That means heat gets trapped in thick sections, leading to uneven cooling during molding and internal stress, and it also means your part will heat up slower but hold heat longer than a metal equivalent. We aim for a consistent wall thickness across the part, between 2mm and 4mm for most injection molded heat resistant plastic parts. If you need a thicker section for strength, build in gradual transitions—no sudden jumps from 2mm to 8mm, that will cause sink marks and internal voids. Instead, taper the thickness over 10-15 times the wall length. For parts that have to be thicker, we often add ribs or gussets to add strength without adding unnecessary bulk or stress. Ribs also help with heat dissipation, because they increase surface area, which is key for parts that run hot. I always say: if you’re designing a plastic part, ribs are your friend. Use them wisely, and you can often get away with a thinner base wall that’s still strong enough.
Thermal cycling is another factor that trips up a lot of designers, especially for parts that go from cold to hot repeatedly. Industrial ovens, automotive components, kitchen appliances—all of these see temperatures swing from room temperature to 150°C or more multiple times a day. Heat resistant plastics expand and contract at a different rate than metal fasteners, which is a common cause of part failure. If you’re using a plastic bracket to mount a metal sensor, make sure the bracket has enough flexibility to accommodate thermal expansion. We often suggest designing mounting holes with a 10% clearance for fasteners, or using self-tapping screws that are rated for heat resistant plastics, instead of metal screws that can put too much stress on the plastic as it expands and contracts. For parts that will undergo repeated thermal shock—like a coffee machine boiler part that goes from 20°C to 120°C in 10 seconds—we test our materials for thermal shock resistance up to 200 cycles, and we recommend using amorphous heat resistant plastics, like polyetherimide (PEI), instead of semi-crystalline ones like PPS. Semi-crystalline plastics have a more defined crystalline structure that can crack when hit with rapid temperature changes, while amorphous plastics flex a little more to absorb the shock.
Prototyping is a step no one should skip, even when you’re working with a supplier of heat resistant plastic. A lot of designers will do a 3D printed prototype, test it at room temperature, and go straight to production, only to find that 3D printed parts have different material properties than molded ones. FDM 3D printed PEEK, for example, has anisotropic strength—meaning it’s weaker along the layer lines, so a part that works at room temperature will crack when heated. We always advise clients to get a molded prototype first, even if it’s a small batch of 50 parts, because molded parts have consistent density, better structural properties, and the same thermal performance as production parts. Last year, a medical device client came to us with a 3D printed prototype of a surgical tool handle, which worked great at room temp. When we molded a test part, it failed at 80°C during a sterilization cycle—turns out the 3D printed handle had 20% less tensile strength at elevated temperatures than the molded version. Switching to molded prototypes saved them $50,000 in tooling costs down the line.
Another thing to consider is chemical exposure, which is tied directly to heat performance. A plastic that handles 150°C in dry air might fail at 120°C if it’s exposed to oil, solvents, or cleaning chemicals. Heat resistant plastics can have different chemical resistance profiles: PPS is great for oil and most industrial chemicals, PEI is better for high temperatures but not as resistant to strong solvents, PA66 with heat stabilizers handles automotive fluids well, but can absorb moisture which reduces its heat resistance. If your part is going to be in contact with chemicals, tell your supplier upfront—we can test material samples under actual operating conditions to make sure they won’t degrade. I once worked with a food service equipment manufacturer who designed a part for a commercial dishwasher, using a standard heat resistant PA66. Within 6 months, the parts were cracking because they were exposed to chlorine-based dishwasher chemicals at 65°C. We switched them to a modified PPS with a chemical stabilizer, and those parts have run for 3 years with zero failures.
Let’s talk about common myths, too, because I hear them all the time. First myth: “All heat resistant plastics are too expensive.” Yeah, high-performance materials like PEEK and PEI cost more than standard plastics, but for many applications, they’re cheaper than metal alternatives. You don’t need to machine aluminum or steel—molded heat resistant plastics can be produced in the same high volumes as ABS, with lower part costs for complex geometries, and they weigh 50-70% less than metal. Second myth: “Heat resistant plastics can replace metal in any application.” No, they can’t. For parts that need to handle 300°C or more, like a jet engine component, you still need ceramic or metal. But for applications up to 250°C, where metal adds unnecessary weight or cost, heat resistant plastic is a perfect alternative. Third myth: “You just pick the highest Tg material.” That’s not true—we worked with a aerospace client last year who wanted a part rated for 200°C, but their part only saw peak temperatures of 120°C, so a 180°C Tg PPS was more than enough, and it cost a third of the 220°C Tg PEI they were considering.
Now, what about production? Designing for injection molding, which is the most common process for heat resistant plastic parts, has its own set of rules. Gates should be placed at the thickest sections of the part to ensure proper material flow, especially for glass-filled materials that can be prone to short shots. Venting is critical, too—trapped air in the mold can cause burns or voids in the part, especially for high-temperature materials that melt at higher temperatures. Our team will work with your mold designer to add vent holes of 0.025mm to 0.05mm along the flow path of the material, which prevents those defects.
At the end of the day, designing with heat resistant plastic isn’t just picking a material with a high temperature rating—it’s understanding your application’s specific needs, matching the right material and form to those needs, and adjusting your geometry and design practices to play to the strength of plastic, not metal.
If you’re designing a part that needs to perform at elevated temperatures, whether it’s an automotive component, industrial machine part, kitchen appliance, medical device, or something else, we can help. Our engineering team will walk through your requirements, test material samples, and work with you to design a part that’s cost-effective, durable, and fits your production needs. Reach out to us to discuss your project details and schedule a consultation.
Electrical Insulation Material References
- Ogorkiewicz, R. M. (1998). Thermoplastics: Properties and Applications. Wiley.
- Rosato, D. V., & Rosato, D. V. (2004). Injection Molding Handbook. Springer.
- Brandrup, J., Immergut, E. H., & Grulke, E. A. (Eds.). (1999). Polymer Handbook (4th ed.). John Wiley & Sons.
- Engineering Design Guide for Thermoplastic Composites. (2010). Society of Plastics Engineers.
- Thermal Properties of Polymers. (2018). National Institute of Standards and Technology (NIST).
Zhejiang Nansu Synthetic Materials Co., Ltd.
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