PAI
also Torlon, Torlon PAI
PAI is a melt-processable amorphous ultra-high-performance thermoplastic (Torlon) with a Tg near 275 °C, supplied as unfilled electrical grade, bearing grade, LF, GF30 and CF30.
Values for the Unfilled (Electrical) condition
PAI grades and fills
PAI is supplied in 5 conditions, soft to hard. Unfilled (Electrical) is the default FabDigit quotes; the values on this page are for it.
Compare all 5 grades and fillsHide
| Grade · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness |
|---|---|---|---|---|---|
Low Friction | PAI compounded with graphite plus PTFE lubricant for the lowest dry-running friction coefficient and low wear at high PV, at the cost of strength and ductility versus unfilled resin. | 110 | 5 | 118 HRM | |
graphite/PTFE lubricated PAI (Torlon 4301/4275/4435 type) | Choose for unlubricated or marginally lubricated wear parts — seal rings, thrust washers, bushings, valve seats — where low friction and high PV matter more than elongation. | 117 | 7 | ||
Unfilled (Electrical)Default Natural/unreinforced PAI | Choose for insulators, connectors and thin-wall parts needing maximum toughness/elongation and the best dielectric properties. | 152 | 15 | ||
30% glass-fiber reinforced PAI | Choose for stiff, dimensionally stable structural parts that must stay electrically insulating at high temperature. | 205 | 7 | ||
30% carbon-fiber reinforced PAI | Choose for the highest stiffness/strength-to-weight and lowest thermal expansion — aerospace brackets, high-speed rotating parts, ESD-tolerant applications. | 205 | 6 |
What is PAI?
PAI is a melt-processable amorphous ultra-high-performance thermoplastic (Torlon) with a Tg near 275 °C, supplied as unfilled electrical grade, bearing grade, LF, GF30 and CF30. At 250 °C continuous service it retains the highest strength, stiffness and creep resistance of any thermoplastic, with excellent wear and chemical resistance; default values are 1.42 g/cm3, 152 MPa tensile strength, 15 % elongation, 4.5 GPa modulus and 0.26 W/m·K thermal conductivity. Limits are high cost, a mandatory staged post-cure to about 260 °C over several days, very high mould and barrel temperatures, and weak long-term resistance to strong alkalis, high-temperature steam and UV. PAI has a density of 1.42 g/cm³ (0.0513 lb/in³), heavier than 83% of polymer grades. Its glass-transition temperature is 275°C (527 °F). PAI has a tensile strength of 152 MPa (22 ksi), stronger than 95% of polymer grades. Elongation at break is 15% and the elastic modulus is 4.5 GPa (0.653 Msi).
What is PAI used for?
- Thrust washers
- Bearings and bearing cages
- Seal rings for aero-engine and hydraulic systems
- Insulating washers and spacers
- High-temperature electrical connectors
- Precision gears
- Wear pads and back-up rings
Advantages
- High service temperature — 250°C (482 °F), better than 94% of polymer grades
- Stiff — 4.5 GPa (0.653 Msi), better than 88% of polymer grades
- Conducts heat well — 0.26 W/m·K (0.15 BTU/hr·ft·°F), better than 77% of polymer grades
- Polishes to a fine finish — 70/100, better than 77% of polymer grades
Limitations
- High embodied carbon — 14 kg CO₂/kg, worse than 95% of polymer grades
- Heavy — 1.42 g/cm³ (0.0513 lb/in³), worse than 83% of polymer grades
- Difficult to weld — 10/100, worse than 82% of polymer grades
- Limited formability — 15/100, worse than 79% of polymer grades
PAI properties
Typical room-temperature values for PAI-Unfilled (Electrical); bars are the position among polymer grades.
Physical4
PAI has a density of 1.42 g/cm³ (0.0513 lb/in³), heavier than 83% of polymer grades. Its glass-transition temperature is 275°C (527 °F).
Mechanical13
PAI has a tensile strength of 152 MPa (22 ksi), stronger than 95% of polymer grades. Elongation at break is 15% and the elastic modulus is 4.5 GPa (0.653 Msi).
Thermal10
PAI is rated for continuous service to 250°C (482 °F). It conducts heat at 0.26 W/m·K (0.15 BTU/hr·ft·°F), better than 77% of polymer grades. Thermal expansion is 31 µm/m·K (17.2 µin/in·°F).
Electrical7
PAI is an electrical insulator with a dielectric strength of 23 kV/mm (584.2 V/mil) and a resistivity of 1×10¹⁵ Ω·m.
Chemical & Environmental3
Corrosion resistance is very good (80/100), worse than 52% of polymer grades. UV resistance is fair.
Sustainability3
Producing a kilogram of PAI takes about 300 MJ of energy and emits 14 kg of CO₂ — more than 97% of polymer grades. Typical recycled content is 0%.
Manufacturability7
PAI's machinability is good (60/100, better than 51% of polymer grades); weldability not recommended (10/100); formability poor (15/100).
Common Calculations4
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the polymer family
Yield strength against density for every polymer grade FabDigit runs. PAI is highlighted; hover a dot for its name, or open the interactive family chart.
Working with PAI
Is PAI easy to machine?
Machines like a hard, abrasive engineering plastic — use sharp carbide or PCD tooling, moderate speeds, light finishing cuts, and machine after post-cure to avoid dimensional drift.
Can PAI be welded?
Not fusion weldable in practice; join by epoxy adhesive bonding, PAI adhesive film, or mechanical fasteners with generous bearing area.
Can PAI be formed, bent or molded?
Injection mold with dried resin at 335–365 °C melt and 200–230 °C mold, then post-cure parts in stages to ~260 °C for several days to develop full strength and chemical resistance.
Manufacturability
The process limits FabDigit's quote engine applies to PAI. Design inside these and the part quotes instantly; outside them it routes to an engineer.
CNC machining
| Machinability | Better60 / 100 |
|---|---|
| ISO material group | N.8 |
| Cutting speed (rough / finish) | 400 / 500 m/min |
| Minimum wall | 0.5 mm |
| Minimum internal radius | 1 mm |
| Drill depth limit | 10× diameter |
| Best surface (machined / polished) | Ra 0.8 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Not Recommend15 / 100 |
|---|---|
| Weldability | Not Recommend10 / 100 |
Injection molding
| Mold shrinkage | — |
|---|---|
| Wall thickness | — – — |
| Recommended draft | — |
| Pre-drying | — |
PAI chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| titanium dioxidepigment/processing aid in unfilled 4203-type grades | ≈ 3 | 3 |
| PTFEinternal lubricant; ~3% in bearing grades | 0.5 – 3 | 0.5 |
| graphitebearing/wear grades only (4301 ≈ 12%, 4275 ≈ 20%) | 0 – 20 | 12 |
| glass fiberGF30 (5030) variant only | ≈ 30 | 30 |
| carbon fiberCF30 (7130) variant only | ≈ 30 | 30 |
| polyamide-imide (trimellitic anhydride +amide-imide backbone; base resin of all grades | balance |
What surface finishes work on PAI?
Natural amber-to-black surfaces polish well and accept plasma or chemical etch before plating/bonding; paint and metallization require thorough drying because of moisture pickup.
Surface treatments FabDigit runs on polymer parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Injection Molding Coating
Organic Coating
Metallization / Functional
Equivalent designations
Standards and trade names that resolve to PAI in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Trade names
- TorlonTorlon PAI
- Also called
- Polyamide-imide
How much does PAI cost?
PAI is a specialty-cost polymer ($$$$$), pricier than about 99% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
PAI — frequently asked
What is PAI used for?
PAI is typically used for thrust washers, bearings and bearing cages, seal rings for aero-engine and hydraulic systems, insulating washers and spacers, high-temperature electrical connectors and precision gears. In short: highest strength carbon-plastic.
What is the tensile strength of PAI?
PAI has a typical tensile strength of 152 MPa (22 ksi) — stronger than 95% of polymer grades. Strength varies by condition: see the 5 listed tempers.
Is PAI easy to machine?
Reasonably — machinability is rated good (60/100, better than 51% of polymer grades). Machines like a hard, abrasive engineering plastic — use sharp carbide or PCD tooling, moderate speeds, light finishing cuts, and machine after post-cure to avoid dimensional drift.
Can PAI be welded?
Not readily — weldability is rated not recommended (10/100). Not fusion weldable in practice; join by epoxy adhesive bonding, PAI adhesive film, or mechanical fasteners with generous bearing area.
What surface finishes work on PAI?
Natural amber-to-black surfaces polish well and accept plasma or chemical etch before plating/bonding; paint and metallization require thorough drying because of moisture pickup.
Can PAI be formed, bent or molded?
Injection mold with dried resin at 335–365 °C melt and 200–230 °C mold, then post-cure parts in stages to ~260 °C for several days to develop full strength and chemical resistance.
What is the maximum service temperature of PAI?
PAI is rated for continuous use to about 250°C (482 °F), and briefly to 280°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does PAI cost?
PAI is a specialty-cost polymer ($$$$$), pricier than about 99% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Can FabDigit make parts in PAI?
Yes — PAI is available for CNC machining, sheet metal and injection molding with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- Torlon PAI Design Guide and grade datasheets (4203L, 4301, 4275, 5030, 7130) — Solvay Specialty Polymers (2021)
- Duratron T4203 / T4301 / T4501 PAI stock shape datasheets — Mitsubishi Chemical Advanced Materials (Quadrant) (2022)
- TECATOR / PAI machinable stock shapes datasheet — Ensinger (2022)
- CAMPUS / UL Prospector polyamide-imide typical property records — CAMPUS Plastics (2023)
- ASM Engineered Materials Handbook Vol. 2: Engineering Plastics — ASM International (1988)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.