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Choosing the right material for plastic parts is no easy task. Many engineers encounter situations where standard plastics like ABS or polycarbonate simply cannot withstand the operating temperatures. Parts may deform, discolor, or even fail completely at high temperatures. This article will explore the properties of heat-resistant plastics and how to select a material that can operate reliably in harsh environments.
Common Types of Heat Resistant Plastics
Heat-resistant plastics are materials that retain their mechanical and physical properties over extended periods at high temperatures (typically above 150°C (302°F)). Unlike ordinary plastics that soften or degrade, these engineered polymers are designed for harsh environments.
The table below summarizes the most common types of heat-resistant plastic materials, their performance limits, properties, and typical applications.
Heat resistant plastics properties
| Material | Continuous use temp | Heat deflection temp (1.82 MPa) | Key characteristics |
| PEEK | 250–260°C | ~160°C (unfilled) / ~300°C (30% GF) | Excellent mechanical strength, chemical resistance, wear resistance, inherently flame retardant V-0 |
| PEI (ULTEM) | 170°C | 190–207°C | Transparent amber, inherently flame retardant V-0, hydrolytic stability, high dielectric strength, passes steam sterilization |
| PPS | 200–240°C | 260–280°C | Excellent chemical resistance, very high stiffness, inherently flame retardant V-0, brittle without reinforcement |
| PSU | 150–170°C | ~174°C | Transparent amber, good hydrolytic stability, withstands repeated steam sterilization, good electricals |
| PPSU | 180–200°C | ~200°C | Exceptional hydrolytic stability, very high impact strength, transparency, withstands repeated autoclave cycles |
| PAI (Torlon) | 250–275°C | >270°C | Highest strength and stiffness among thermoplastics, excellent wear resistance, low creep, >120 MPa tensile strength |
| PI (Vespel) | 260–350+°C | >360°C | Exceptional thermal stability, low coefficient of thermal expansion, excellent electrical insulation, very difficult to injection mold |
| LCP | 220–260°C | 230–340°C | Extremely high flow, good chemical resistance, very low moisture absorption, thin wall capability down to 0.1mm |
| PTFE (Teflon) | 260°C | ~120–150°C | Lowest coefficient of friction, almost universal chemical resistance, excellent non stick, does not melt flow for injection moulding |
| High temperature PA (PA46, PA6T, PA9T, PPA) | 120–170°C | 120–300°C | Good balance of mechanical performance and processability, cost effective |
Injection molding difficulty comparison
| Material | Processing difficulty |
| PEEK | High: requires melt temp 370–400°C, mold temp 160–200°C |
| PEI | Medium: melt temp 350–380°C, mold temp 140–165°C |
| PPS | Medium high: melt temp 300–340°C, mold temp 130–160°C |
| PSU/PPSU | Medium: melt temp 350–390°C, mold temp 120–160°C |
| LCP | Medium: melt temp 280–340°C, mold temp 35–150°C |
| PTFE | Very high: does not melt flow; requires compression moulding or ram extrusion, not suitable for standard injection moulding |
| High temperature PA | Low medium: melt temp 280–320°C, mold temp 80–130°C |
Injection Molding Challenges and Solutions for Heat Resistant Plastics
Processing heat resistant plastics is fundamentally different from standard resins. Understanding the main challenges helps manufacturers plan equipment requirements and avoid common defects.Working with a heat molding plastic such as PEEK or PPS requires melt temperatures above 300°C, which standard machines cannot achieve.
High melt and mold temperatures
The maximum barrel temperature of a standard injection molding machine is typically 300°C, and the mold temperature is 100°C to 120°C. However, PEEK material requires a melt temperature of 370°C to 400°C and a mold temperature of 160°C to 200°C. Therefore, specialized high-temperature equipment is needed, including a corrosion-resistant barrel, a screw with a high-temperature heater, and an oil- or electronic mold temperature controller capable of maintaining a stable mold temperature above 200°C.
Corrosion and wear risks
PPS releases trace amounts of hydrogen sulfide gas when processed above 300°C. This corrosive gas will erode standard steel screws and mold cavities, potentially causing severe wear within 200 hours. Therefore, it is crucial to use corrosion-resistant alloys such as Hastelloy or to apply a protective coating such as titanium nitride to the screw. Ventilation and exhaust systems must be adequate to remove the corrosive gases.
Moisture sensitivity
Most high-temperature engineering plastics are hygroscopic. Polyethyleneimine (PEI) must be dried at 150°C for 4 to 6 hours. Polystyrene (PPS) needs to be dried at 140°C to 150°C for 3 to 4 hours to bring the residual moisture content below 0.05%. Insufficient drying can lead to cracks, bubbles, surface defects, and material degradation.
Dimensional stability and shrinkage
The final properties of semi-crystalline materials (such as PPS) are largely dependent on the mold temperature. Molding PPS at lower mold temperatures of 80°C to 100°C results in lower crystallinity. The heat deflection temperature at this temperature may only reach 175°C, while with a suitable mold temperature of 130°C to 160°C, the heat deflection temperature can reach 260°C. Furthermore, parts molded at insufficient temperatures may exhibit post-molding shrinkage and dimensional changes after annealing.
High injection pressure requirements
The injection pressure required to fill thin sections with high-temperature resins is much higher than that for ordinary plastics. Using a screw designed specifically for heat-resistant polymers, maintaining a high injection speed, and using large-sized gates and runners help reduce pressure loss.
Industry Applications
In many industries, heat-resistant plastics are now standard, whereas metal was once the only option. Below are some key industries and their applications for these materials:
- Aerospace: PEEK is used for structural supports and engine components; PEI (compliant with FAR25.853) is used for cabin interiors; PI films (such as Kapton) are used for extreme thermal insulation.
- Automotive: PPS is used in EGR systems and turbocharger piping; high-temperature polyamides are used in engine hoods and thermostat housings for weight reduction.
- Medical Devices: PEEK is used for implants; PEI, PSU, and PPSU are used for housings that can withstand repeated steam or gamma ray sterilization.
- Electronics: LCP is used for miniature connectors; PEEK is used for high-frequency insulation; PEI is used to maintain stable performance across a wide range of humidity and temperature.
- Industrial and Chemical Processing: PTFE and PPS are used for chemical resistance; PEEK/PAI is used for wear-resistant bearings and seals; PPS is used for pump impellers.
- Consumer Products: Polytetrafluoroethylene (PTFE) for non-stick coatings; transparent heat-resistant plastics for oven-safe cookware and appliance housings.
How to Choose the Right Heat Resistant Plastic
Not every heat resistant plastic is suitable for every application. Selecting the wrong material may result in component failure, higher costs, or injection molding challenges. The following six key factors help you narrow down material choices according to actual operational requirements.
Maximum continuous use temperature
- Above 260°C: PI or PBI
- 200–260°C: PEEK
- 150–200°C: PEI, PPS, PPSU
- 120–150°C: High‑temperature polyamides
Chemical exposure
- Broad chemical resistance: PPS, PTFE
- Good resistance + strength: PEEK
- Automotive fluids/hydrocarbons: PPS
Mechanical load and wear
- High load/creep resistance: PAI
- Fatigue and wear: PEEK
- High stiffness: Glass‑filled PPS
- Bearing applications: Bearing‑grade PEEK, PAI, or PTFE compounds
Moulding feasibility
- PEEK needs melt up to 400°C, mould up to 200°C – requires specialised equipment.
- LCP has high flow but anisotropic properties.
- PPS needs high mould temperature for full crystallinity.
Regulatory needs
- Medical: USP Class VI or ISO 10993 (PEEK, PPSU, PEI, certain PPS).
- Aerospace: UL 94 V‑0, low smoke toxicity, OEM approvals.
- Food contact: FDA compliance (PEI, PPS have approved grades).
Work With an Experienced Injection Molding Manufacturer
Producing parts from heat resistant plastics requires close collaboration between design, molding, and material experts. HingTung supports high temperature projects in four key areas:
DFM analysis and risk identification
We utilize mold flow simulation to review part geometry, gate location, and cooling balance before mold making begins, identifying problems early.
Material and equipment matching
We help you select the right materials to meet your production volume and performance requirements. Our expertise allows us to heat and mold plastic parts with tight tolerances, even for high-temperature grades like PEI and PEEK.
Full lifecycle cost and lead time optimization
We manage the entire production process, from soft molds for validation to hardened multi-cavity molds for high-volume production.
FAQs
What temperature range classifies plastic as heat resistant?
Plastics capable of continuous service above 150°C are generally considered heat resistant. Some high performance materials operate above 250°C.
Which heat resistant plastic is easiest to injection mould?
PEI and PPSU offer good flow and thermal stability while providing 170°C to 200°C heat resistance, making them easier to mould on standard high temperature equipment. PPS requires careful mould temperature control but provides good flow. PEEK is the most challenging among commonly used high temperature plastics.
What is the maximum temperature PEEK can withstand?
PEEK has a long term continuous use temperature of 260°C, a glass transition temperature of 143°C, and a melting point of approximately 343°C. It can withstand 300°C for short periods without losing most mechanical properties.
Why does PPS need a high mould temperature?
PPS is a semi crystalline polymer. When moulded at low temperature (such as 80°C to 100°C), the polymer chains cannot arrange into a highly ordered crystalline structure. This results in low crystallinity parts with lower heat deflection temperature and dimensional stability. High mould temperatures of 130°C to 160°C allow proper crystal formation, achieving the full heat deflection temperature of 260°C.
Conclusion
Heat resistant plastics have enabled modern engineering designs in aerospace, automotive, medical, and electronics industries that were previously impossible or impractical with metals alone. From PEEK and PEI to PPS and high temperature polyamides, each material offers a specific balance of thermal stability, mechanical strength, chemical resistance, and processability. Choosing the right heat resistant plastic material depends on the operating temperature, chemical exposure, mechanical load, production volume, and budget.
Working with an experienced injection moulding suppliers helps avoid the high costs of material degradation, dimensional variation, and part failure from improper material or process selection. Whether launching a new high temperature component or optimising an existing design, HingTung provides material selection guidance, DFM analysis, tooling, and manufacturing expertise to bring reliable heat resistant plastic parts to market efficiently.