Compared to traditional materials such as metals, ceramics, and laminated glass, plastic has the disadvantage of relatively low heat resistance, which typically limits its use in high-temperature environments. This characteristic stems from the molecular composition of plastics, which can soften or degrade more readily under heat stress.
Among plastic materials, different types exhibit varying levels of heat resistance; some have poor high-temperature tolerance, while others perform significantly better. High-temperature plastics are generally defined as those with a Heat Deflection Temperature (HDT) above 200 °C.
The principal metrics for evaluating the heat resistance of plastic products include Heat Deflection Temperature (HDT), Vicat Softening Temperature (VST), and Continuous Service Temperature or the Relative Thermal Index (RTI). Among these, HDT is the most commonly used. For a given plastic, the relative sequence of these heat-resistance parameters typically is: Vicat Softening Temperature > Heat Deflection Temperature > Continuous Service Temperature (e.g. RTI or related index).
Types of Heat-Resistant Plastics
Plastics can be classified by their long-term service temperature into three categories: commodity (general-purpose) plastics, engineering plastics, and high-temperature engineering plastics (also known as heat-resistant plastics, high-performance plastics, or specialty engineering plastics).
- Commodity (General-Purpose) Plastics: Typical long-term use temperature: below 100 °C. Common examples include PE, PP, PS, PVC, and ABS, which are used in packaging, daily household items, and toys.
- Engineering Plastics: Long-term service temperature: approximately 100 °C to 150 °C. Typical examples include PA, POM, PBT, PC, and PPO. These are typically used in mechanical components, automotive parts, and electrical/electronic devices.
- High-Temperature Engineering Plastics: Long-term service temperatures above 150 °C and offer excellent thermal resistance, flame retardancy, aging resistance, dimensional stability, machinability, and electrical performance. As top-tier plastics, they can replace metals.
Top 5 Heat Resistant Plastic Materials
Selecting the right material for high-temperature applications can make all the difference in performance and durability. Below are the five most commonly used heat-resistant plastics that excel in withstanding extreme temperatures without compromising structural integrity.
PAI (Polyamide-imide)
PAI is known for its impressive thermal stability and can handle continuous exposure to temperatures up to 260 °C (500 °F). This material is ideal for applications that require both high thermal and mechanical strength.
Key Benefits:
- Superior mechanical strength and rigidity
- Excellent wear resistance and low friction
- Outstanding resistance to chemicals and radiation
- High electrical insulating properties
PAI is used in aerospace, automotive, and industrial applications, including bearings, gears, electrical connectors, and seals, where high temperatures and mechanical stress are prevalent.
PTFE (Polytetrafluoroethylene)
PTFE, often referred to as Teflon™, can maintain its physical properties at temperatures as high as 260°C (500°F) for continuous exposure and maintains dimensional stability. This material can even withstand short-term thermal exposure up to 300°C (572°F) without showing signs of degradation. This is due to its strong carbon-fluorine bonds, which resist thermal degradation. But its tensile strength and elongation can decrease at high temperatures.
Key Benefits:
- Superior chemical resistance
- Non-stick and low friction properties
- Excellent electrical insulation
- High dimensional stability
PTFE is commonly used in chemical processing industries, as well as in food production, automotive applications, and electrical industries for seals, gaskets, bearings, and insulating components.
PEEK (Polyether Ether Ketone)
PEEK (Polyether ether ketone) can maintain continuous operation up to 250°C (482°F) and can briefly withstand up to 310°C (590°F) without significant degradation. PEEK’s thermal stability and V-0 flammability rating ensure minimal degradation, even in extreme environments, and it exhibits strong resistance to a variety of chemicals.
Key Benefits:
- High chemical and radiation resistance
- Outstanding mechanical properties (high tensile strength, low wear)
- Superior dimensional stability under stress
- Excellent fatigue resistance and low friction
- Low coefficient of thermal expansion for dimensional stability
PEEK is widely used in industries like aerospace, automotive, and medical fields, particularly for components such as seals, bearings, connectors, and valves.
PPS (Polyphenylene Sulfide)
PPS is a high-temperature thermoplastic known for its impressive resistance to heat, chemicals, and oxidation. Its semi-crystalline structure supports upports performance retention at temperatures up to 220°C – 230°C (428°F – 446°F ). Its inherent resistance to oxidation helps limit material deterioration during prolonged thermal exposure.
Key Benefits:
- High dimensional stability and mechanical strength
- Excellent electrical insulation properties
- Long-term thermal stability
PPS is frequently used in automotive, electrical, and chemical processing industries, particularly for components like pumps, valves, and electrical connectors that are exposed to high temperatures and harsh conditions.
PEI (Polyetherimide, Ultem)
Polyetherimide (PEI), also known as Ultem, is an amorphous thermoplastic. This material has an extremely high melting point of 219°C (426°F) and a maximum continuous service temperature of 170°C (338°F). PEI offers excellent resistance to high-energy radiation, hydrolysis, and a range of chemicals, though it can be attacked by strong bases.
Key Benefits:
- Excellent mechanical strength and rigidity
- Good electrical insulating properties
- Resistant to a broad range of chemicals
- High dimensional stability under heat and stress
PEI is frequently used in aerospace, automotive, electrical, and medical industries for connectors, insulators, and structural components that require both heat and electrical resistance.
Tips to Choose High-Temperature Plastics
Choosing the right high-temperature plastic involves evaluating the conditions the material must withstand and the demands of the intended application.
- Operating temperature: Match the material to the maximum and minimum service temperatures. PEEK and polyimide suit higher-temperature conditions, while PEI and PPS suit some lower ranges.
- Mechanical load and stress: Evaluate tensile strength, impact resistance, and wear. PEEK suits high-stress applications, while PTFE works well in low-friction applications.
- Chemical exposure: Check compatibility with chemicals, solvents, and oils. PTFE and PPS offer broad chemical resistance.
- Electrical requirements: For electrical insulation, consider materials such as polyimide and PEI with suitable dielectric properties.
- Flame resistance: Check the required flame-retardancy rating. PEI and PPS can meet certain flame-resistance requirements, depending on the grade.
- Dimensional stability: Consider thermal expansion and dimensional changes under heat or mechanical stress. PPS and PEEK can suit precision applications.
- Cost and availability: Balance performance with budget and material availability. PPS and PEI may offer lower-cost alternatives to PEEK in some applications.
- Processing requirements: Confirm compatibility with injection molding or CNC machining. PEEK and PEI can be machined, while PTFE often requires specialized processing.
Challenges in Using Heat-Resistant Plastics
While heat-resistant plastics offer exceptional performance in high-temperature applications, their use does come with certain challenges. These include processing difficulties, compatibility with other materials, and the risk of wear and tear under extreme heat conditions.
They are Difficult to Process and Mold
One of the main challenges with high-temperature plastic materials is their processing complexity. High-performance thermoplastics such as PEEK and PAI often require specialized processing equipment due to their high melting points. In many cases, these may need to be processed at even higher material temperatures and pressures, which are difficult to achieve with standard injection molding equipment. This can significantly increase production costs and lead times.
Moldability is also a concern, as some heat-resistant plastics tend to have poor flow properties, and the high viscosity of these plastics at elevated temperatures makes it difficult to uniformly fill the mold, making it difficult to form complex geometries or fine-detail molded parts. This may require more advanced mold design or post-processing work to achieve the desired results.
They Are Not Easy to Comply with Other Materials
In many applications, heat-resistant plastics often combine with other materials, such as metals or other plastics. Ensuring compatibility between different materials, especially when exposed to high temperatures, can be tricky. Some high-temperature thermoplastics may have expansion rates or thermal conductivities that differ significantly from those of other materials, leading to injection molding defects like warping, cracking, or delamination during temperature fluctuations.
Additionally, heat-resistant plastic materials may not adhere well to certain metals or other types of plastics, making it difficult to achieve strong bonds without additional adhesives or surface treatments. These compatibility issues must be carefully considered during the design and material selection process to ensure long-term functionality and durability.
May Get Wear and Tear Under High Temperatures
While high-temperature resistant plastics can withstand extreme temperatures, they are not immune to wear and tear. Under continuous exposure to high temperatures, even the most heat-resistant plastics can experience degradation of their properties, such as reduced tensile strength and impact resistance, and a lack of surface integrity. This is especially true for plastics that are used in environments where they are subjected to constant mechanical stress or abrasive environments.
Over time, the combination of high heat and physical wear can lead to material fatigue. For example, polyphenylene sulfide (PPS) and polyimide (PI), while very strong at high temperatures, can still suffer from microcracks, discoloration, or dimensional stability loss under thermal cycling or friction. To mitigate these effects, regular monitoring and maintenance are critical in environments where high-temperature plastics are used for extended periods of time.
These challenges highlight the importance of choosing the right material for your application. For more guidance, read our article on 6 common mistakes in plastic material selection.
Choose an Expert Manufacturer to Help With Material Selection
The importance of selecting the appropriate heat-resistant plastic cannot be overstated in high-performance applications. Choosing the right material ensures optimal performance under demanding conditions, maintaining both the physical and mechanical integrity of the product over time. Whether for aerospace, automotive, or electronics, the correct high-temperature plastic material can make a substantial difference in the reliability and longevity of the components. For complex requirements, consulting with material experts or suppliers can provide additional insights and recommendations.
If you’re looking for expert advice and high-quality solutions, Erye, the molding material expert, is here to guide you every step of the way. Contact us today for a quote!
