PAI Torlon: Properties, Uses & Cost Guide
Tensile data verified against MatWeb.com database & manufacturer datasheets · Last updated July 2026
Published: 2026-05-27
Polyamide-imide (PAI), commercially known as Solvay Torlon, occupies the performance space between PEEK and polyimide (Vespel)—offering higher strength and temperature resistance than PEEK without the extreme processing difficulty and cost of...
Polyamide-imide (PAI), commercially known as Solvay Torlon, occupies the performance space between PEEK and polyimide (Vespel)—offering higher strength and temperature resistance than PEEK without the extreme processing difficulty and cost of Vespel. PAI delivers the highest tensile strength of any unreinforced thermoplastic (130 MPa for Torlon 4203) and maintains useful mechanical properties to 260°C continuous service. Its exceptional creep resistance, low coefficient of thermal expansion (CTE ~25 ppm/°C), and outstanding wear resistance make it the material of choice for aerospace thrust washers, automotive transmission seals, and semiconductor test sockets.
PAI requires a complex post-cure cycle after molding to achieve full mechanical properties. Green (as-molded) parts must undergo a stepped temperature cure program lasting up to 7 days, progressively heating from 150°C to 260°C in controlled increments. This post-cure drives off residual NMP solvent and completes the imidization reaction—without it, the part will have only 50-60% of its rated strength and will outgas excessively at elevated temperature. Torlon 4301 (PTFE-filled) provides the best wear and friction properties for bearing applications; Torlon 5030 (30% glass fiber) offers maximum stiffness and load-bearing capacity.
Recommended Applications
PAI Torlon is commonly specified for:
⚠ Not Recommended For
PAI Torlon is not recommended for:
- Moisture exposure above 200°C without pre-drying (PAI absorbs moisture → steam blistering during processing)
- Applications requiring low friction without lubrication (PAI has high friction; add PTFE/graphite fillers)
- Cost-sensitive applications where PEEK suffices (PAI is 1.5-2× the cost of PEEK with marginal property gains in many cases)
Selection & Application Guide
Torlon (PAI) is the strongest and hardest unfilled thermoplastic available, with a continuous service temperature up to 260°C and exceptional creep resistance. Choose Torlon over PEEK when maximum strength at elevated temperature is required — Torlon's tensile strength (150-200 MPa) exceeds PEEK's 100 MPa by 50-100%. Torlon also outperforms Ultem in temperature capability by 40°C. The trade-off: Torlon requires post-curing after molding and is significantly more difficult to process.
Real-World Applications
Torlon's combination of strength, temperature resistance, and low flammability makes it suitable for jet engine bushings, seals, and thermal isolators where metal replacement reduces weight.
Torlon 4301 (bearing grade with PTFE/graphite fillers) provides the lowest wear rate of any thermoplastic, making it the choice for high-speed, unlubricated gear trains.
Torlon's low outgassing and dimensional stability at elevated temperatures suit it for wafer transport components and test sockets in semiconductor manufacturing.
Torlon 4275 and 4630 grades with internal lubricants provide exceptional PV limits for continuous-duty thrust washers in hydraulic and pneumatic systems.
Processing & Cost Considerations
Manufacturing Tips
- Torlon requires injection molding at melt temperatures of 340-370°C with mold temperatures of 230-280°C — even more demanding than PEEK. After molding, parts must be post-cured in an oven for up to 5 days in staged temperature increases to achieve full mechanical properties.
- The post-cure process is critical: moldings without post-cure have only 30-40% of their final strength. Standard post-cure cycle involves step-wise temperature increases from 150°C to 260°C over 3-5 days. This adds significant processing cost and lead time.
- Torlon machines well with carbide tooling and is often supplied as extruded rod and plate stock for CNC machining — common for low-volume aerospace parts where molding tooling cannot be justified.
Torlon is among the most expensive engineering thermoplastics at $80-120/kg for unfilled grades, with bearing grades reaching $150-200/kg. Post-curing adds 3-5 days to production cycle time and requires dedicated oven capacity. Total processing cost including post-cure can be 2-3× the raw material cost. Despite the price, Torlon is cost-effective when it replaces metal components in weight-critical aerospace applications or when its wear resistance eliminates the need for external lubrication systems.
Technical Properties
| Density | 1.41 g/cm³ |
|---|---|
| Tensile Strength | 130 MPa (unfilled); 200 MPa (30% GF) |
| Melting Point | N/A (Amorphous, Tg 275°C) |
| Shrinkage Rate | 0.6-0.8% |
| Flexural Modulus | 5.0 GPa |
| Hdt | 278 °C at 1.82 MPa |
| Continuous Service Temp | 260 °C |
Engineering Tool: Shrinkage & Cost Estimator
Calculate part weight, mold cavity dimensions accounting for shrinkage, and material cost — all locally in your browser.
Equivalents & Cross-References
| Equivalent / Alternate | Action |
|---|---|
| Solvay Torlon 4203 | |
| Torlon 4301 (PTFE-filled) | |
| Torlon 5030 (30% GF) |
Frequently Asked Questions
What is the post-cure requirement for Torlon PAI and why is it critical?
Torlon PAI requires a mandatory post-cure cycle after injection molding—this is not optional. Green parts contain residual N-methyl-2-pyrrolidone (NMP) solvent from the polymerization process and have incomplete imidization. The post-cure program typically runs 5-7 days: ramp from 150°C to 260°C in 5-10°C increments, holding at each step for several hours. Without post-cure: (1) tensile strength is reduced by 40-50%, (2) the part outgasses NMP at elevated temperatures contaminating sensitive environments (semiconductor, aerospace), and (3) dimensional stability is compromised as the part continues to cure in service. Always verify post-cure completion by measuring glass transition temperature—fully cured Torlon reaches Tg 275°C.
How does PAI Torlon compare to PEEK for wear and friction applications?
Torlon 4301 (PTFE-filled) outperforms unfilled PEEK in wear resistance by approximately 3-5× in dry sliding conditions against steel. Its PV limit (pressure × velocity) at 100 fpm is approximately 30,000 psi·fpm versus 15,000 psi·fpm for unfilled PEEK. However, Torlon is 2-3× the raw material cost of PEEK and requires the 7-day post-cure cycle, adding significant lead time. For moderate wear applications below 200°C, bearing-grade PEEK (with PTFE/graphite) is often the more economical choice. Specify Torlon when the combination of high load, continuous temperature above 200°C, and maximum wear life justifies the cost premium.
How does Torlon compare to Vespel polyimide?
Torlon (PAI) is melt-processable by injection molding; Vespel (PI) requires compression molding and sintering. Vespel offers higher continuous service temperature (up to 310°C vs 260°C for Torlon) and better electrical properties, but Torlon has higher tensile strength and impact resistance. Choose Torlon for complex geometries via molding; choose Vespel for extreme temperature or electrical insulation.
Why does Torlon require post-curing?
Torlon undergoes additional imidization reactions after molding that increase molecular weight and crystallinity. The molded part has only partial imidization; the staged post-cure completes the reaction, increasing tensile strength from ~100 MPa to 150-200 MPa and raising the glass transition temperature from ~190°C to ~275°C. Without post-cure, the part will not achieve its rated properties.
Can Torlon be used for bearings without external lubrication?
Yes. Torlon bearing grades (4301, 4275, 4630) contain PTFE and graphite internal lubricants that provide self-lubricating performance. Torlon 4301 has a PV limit of 1,000,000 psi-fpm — one of the highest of any polymer. This makes it suitable for dry-running bearings, bushings, and wear rings in pumps and compressors.
Is Torlon resistant to hydraulic fluids?
Yes. Torlon has excellent resistance to hydraulic fluids (Skydrol, MIL-H-5606), synthetic oils, and aviation fuels. This chemical resistance, combined with its mechanical strength, makes Torlon a standard material for hydraulic and fuel system components in aerospace applications.
What is the difference between Torlon and Ultem?
Torlon (PAI) and Ultem (PEI) are both high-temperature amorphous polymers, but Torlon offers significantly higher performance at higher cost. Torlon's Tg is 275°C vs 217°C for Ultem; Torlon's tensile strength is 150-200 MPa vs 105 MPa for Ultem. Torlon requires post-curing; Ultem does not. Choose Ultem when 180°C service temperature is sufficient; choose Torlon for extreme conditions above 200°C.
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References & Industry Standards
- ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
- UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
- MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
- ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org