How hot can each material go? A practical comparison
Why Temperature Ratings Matter
The continuous service temperature (CST) is one of the most frequently misused specifications on material datasheets. CST assumes minimal mechanical load and no chemical exposure — real applications layer on thermal cycling, creep loads, and environmental factors that significantly lower the practical ceiling.
This guide provides temperature comparison data and explains what the numbers actually mean for your application.
Temperature Comparison Table
| Material | Continuous Service | Tg | Melting Point | HDT (1.8 MPa) |
|---|---|---|---|---|
| PI | 300°C+ | 280–360°C | None (thermoset-like) | 280°C+ |
| PAI (Torlon) | 275°C | 275°C | None (amorphous) | 274°C |
| PTFE | 260°C | −97°C (crystalline) | 327°C | – |
| PEEK | 260°C | 143°C | 341°C | 162°C |
| PPS | 220°C | 90°C | 280°C | 135°C |
| PPSU | 180°C | 220°C | None (amorphous) | 207°C |
| PEI (Ultem) | 170°C | 217°C | None (amorphous) | 210°C |
| PSU | 160°C | 187°C | None (amorphous) | 174°C |
| PVDF | 140°C | −35°C | 171°C | 112°C |
| PET-P | 120°C | 75°C | 255°C | 80°C |
| POM (Acetal) | 100°C | −60°C | 175°C | 110°C |
| PA66 (Nylon) | 100°C | 50°C | 260°C | 90°C |
Understanding Temperature Measurements
Continuous Service Temperature (CST)
The maximum temperature at which a material can operate continuously without significant degradation. This assumes minimal mechanical load, no chemical exposure, and static conditions — ideal for comparison but rarely achievable in real applications.
Glass Transition Temperature (Tg)
The temperature at which an amorphous polymer transitions from rigid/glassy to soft/rubbery. For semi-crystalline materials (PEEK, POM, PA), the crystalline structure provides mechanical integrity above Tg. For amorphous materials (PAI, PEI, PPSU), performance above Tg degrades rapidly.
Heat Deflection Temperature (HDT)
The temperature at which a material deflects by 0.25mm under a specified load (typically 0.45 MPa or 1.82 MPa). HDT is closer to real-world performance than CST — especially for load-bearing applications.
Thermal + Mechanical Load: The Critical Factor
A PEEK part at 200°C with a constant 20 MPa load behaves very differently from the same PEEK part at 200°C with no load. When comparing materials, look at HDT under load and request creep modulus data at your specific operating temperature for load-bearing applications.
Quick Selection Guide
| If you need… | Choose |
|---|---|
| Highest temperature (>260°C) | PI or PAI |
| 250–260°C with structural load | PEEK |
| 200–250°C (cost-sensitive) | PPS |
| 170–200°C with impact resistance | PPSU |
| 160–170°C (best value) | PEI (Ultem) |
| Up to 140°C with chemical resistance | PVDF |
Frequently Asked Questions
What happens if a plastic exceeds its continuous service temperature?
Exceeding CST accelerates degradation. Semi-crystalline materials may lose crystallinity and soften. Amorphous materials may deform under load. Chemical resistance also decreases at elevated temperatures.
Should I use CST or HDT for material selection?
Use HDT for load-bearing applications and CST for non-loaded applications. For structural parts operating at temperature, request creep data — it’s the most reliable predictor of long-term performance.
Can I use PEEK at 260°C continuously?
Yes, in non-load applications (chemical exposure, minimal mechanical stress). For load-bearing applications at 260°C, consider PAI or reduce the design load. After 5,000 hours at 260°C, PEEK retains nearly full initial strength.
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