PAI vs PEEK: Choosing Between the Two Strongest Engineering Plastics

PAI (Torlon) and PEEK are both top-tier engineering thermoplastics, but they earn their keep in different corners of the performance envelope. I've watched engineers default to PEEK because it's the "safe" choice, when PAI would have been the better technical answer.

Here's when PAI actually beats PEEK — and when it doesn't.

The headline numbers

PAI's glass transition temperature of 275°C substantially exceeds PEEK's 143°C. PAI also maintains higher strength and stiffness at extreme temperatures. Continuous service for PAI is rated at 260°C, same as PEEK, but PAI retains more of its room-temperature properties as you approach that ceiling.

Unfilled PAI has about 50% higher compressive strength than unfilled PEEK (220 MPa vs 150 MPa). The stiffness is about the same, but PAI's thermal performance — particularly its ability to hold dimensions at extreme temperatures — separates it.

The trade-off: PAI is more brittle than PEEK, harder to machine, and more expensive. You choose PAI when the temperature-performance benefit outweighs these costs.

Where PAI wins

Extreme heat with load. Above 230°C, PAI is simply stronger than PEEK. At 260°C, PAI still carries meaningful structural load while PEEK is approaching its limits. Aerospace engine components, downhole oil tools, and high-temperature test fixtures are classic PAI territory.

Wear at high temperature. PAI's wear resistance holds up better than PEEK's as temperature climbs. For high-temperature bearings and bushings in continuous operation, PAI often outlasts PEEK by 2-3x. The material is inherently lubricious — graphite-filled grades of PAI (like Torlon 4301) are genuinely impressive in dry-running applications.

Dimensional stability. PAI has a very low and very linear CTE. Parts that must hold precise dimensions across wide temperature swings (aerospace instrumentation, semiconductor metrology fixtures) favor PAI.

Strength-to-weight at temperature. PAI is slightly denser than PEEK (1.41 vs 1.32 g/cm³), but its higher specific strength at elevated temperature makes it the choice for weight-critical hot applications.

Where PEEK wins

Toughness and impact. PEEK stretches 30-50% before breaking. PAI stretches about 6-12%. Snap-fits, clips, and anything that sees impact or shock loading belong in PEEK. A PAI part under the same conditions cracks.

Chemical resistance. Both are excellent, but PEEK edges PAI in some aggressive environments — particularly steam, hot water, and strong bases. PAI can hydrolyze in prolonged hot water or steam exposure. For autoclave-sterilized medical devices, PEEK is the default for this reason.

Machinability. PEEK is more forgiving to machine. PAI is harder, more abrasive, and more susceptible to edge chipping and micro-cracking. It demands sharper tools, lighter cuts, and more careful thermal management. The machining cost difference is real.

Cost. PAI stock shapes cost 30-50% more than equivalent PEEK shapes. Between the raw material premium and the harder machining, a PAI part typically costs 40-70% more than the equivalent in PEEK.

The edge cases

Wear components. Both are excellent in wear grades, but they behave differently. PAI wear parts (especially graphite-filled) have lower friction and longer life at high temperature, but are more sensitive to edge loading and impact. A PEEK bearing survives some misalignment and shock. A PAI bearing under the same conditions may crack or chip at edges.

Electrical. Both are outstanding insulators. PAI has slightly higher dielectric strength. For most applications, it's a wash.

Flammability. Both are V-0 rated. Both meet aerospace FST requirements. Not a differentiator.

How we decide

If the application runs above 230°C and carries structural or wear load, PAI is the right answer technically. The cost premium is real, but the performance gap at those temperatures is wide enough to justify it.

If the application sees impact, steam, or hot water — or if toughness is essential — PEEK is the safer bet.

If you're in the middle and cost is the tiebreaker, PEEK usually wins because the machining savings stack on top of the material savings.

We stock both and can help you decide. Send the drawing and tell us what temperature and loads your part sees. We'll give you a recommendation based on what works in the real world.