If you read our Ultem® vs. PEEK comparison, you already know those two resins cover most of the "we need more than nylon" conversations that come through our shop. But there's a third material that outperforms both of them on strength and heat. It just comes with trade-offs of its own. This is where Torlon® polyamide-imide fits into the picture, and why it's worth understanding before you spec a part.
- Torlon® PAI wins on strength, stiffness, and continuous-use temperature, the highest of any melt-processable thermoplastic. Best for extreme mechanical and thermal loads.
- PEEK is the generalist: strong, chemically resistant, proven in aerospace and medical, and easier to source and machine than Torlon®.
- Ultem® (PEI) is the value play: strong and heat-resistant enough for most jobs, at a lower cost and easier machinability than either PAI or PEEK.
Three materials, three different reasons to exist
Torlon® PAI
Solvay's PAI resin combines thermoset-level strength with thermoplastic processability. It's injection molded or machined, then oven-cured to reach full properties. Built for the applications other plastics can't survive.
PEEK
A semi-crystalline thermoplastic with an established track record in aerospace, oil & gas, and medical implants. Strong, chemically stable, and melt-processable without a post-cure step.
Infographic: continuous-use temperature
Thermal ceiling is usually the first filter. Here's where each resin's long-term service temperature actually lands.
How the numbers compare
Pulled from Emco's own PEEK and Ultem® product pages and Solvay's Torlon® 4203 data sheet, all unfilled/general grades at room temperature.
| PROPERTY | TORLON® 4203 | PEEK (unfilled) | ULTEM® 1000 (PEI) |
|---|---|---|---|
| Tensile strength | 20,000 psi | 16,000 psi | 16,500 psi |
| Flexural modulus | 600,000 psi | ~500,000 psi | 500,000 psi |
| Compressive strength | 24,000 psi | 20,000 psi | 22,000 psi |
| Heat deflection temp. (264 psi) | 532°F / 278°C | 320°F / 160°C | 392°F / 200°C |
| Max continuous operating temp. | 500°F / 260°C | 480°F / 249°C | 340°F / 171°C |
| Dielectric strength | 580 V/mil | 480 V/mil | N/A |
| Flammability (UL94) | V-0 | V-0 | V-0 |
| Processing | Molded/machined, then post-cured | Molded or machined, no post-cure | Molded or machined, no post-cure |
Infographic: where each material actually wins
Raw numbers don't tell you about cost or how easy a material is to machine into your part. This is the trade-off view.
When to choose which
Choose Torlon®
When the part has to survive conditions that would soften or creep in anything else.
- Continuous service above 400–500°F
- High compressive or wear loads (bearings, seals, wear rings)
- Metal-replacement parts needing steel/aluminum-like dimensional stability (filled grades)
The right material is the cheapest one that survives the application, not the strongest one on the data sheet.
In practice, most parts that "need Torlon®" only need it at the hottest, highest-load point in the assembly, and the rest of the design can run on Ultem® or even a lower-cost engineering plastic. Before you spec an entire part in the top-tier material, it's worth a conversation about where the real stress actually lives.