Ultem (PEI) vs PEEK: Premium Engineering Plastics Compared

Ultem is the flame-retardant champion certified for aircraft interiors with inherent self-extinguishing properties. PEEK offers higher temperature resistance and chemical inertness for the most extreme environments.

Side-by-Side Property Comparison

PropertyUltem (PEI)PEEK (Polyether Ether Ketone)
Tensile Strength85 MPa (12.3 ksi)100 MPa (14.5 ksi)
Yield Strength85 MPa (12.3 ksi)91 MPa (13.2 ksi)
HardnessRockwell M109Rockwell M99
Density1.27 g/cm³1.31 g/cm³
Machinability Rating55/10060/100
Thermal Conductivity0.22 W/m·K0.25 W/m·K
Melting Point217 °C (Tg)343 °C
Tolerance±0.02 mm±0.02 mm

Key Differences

PropertyUltem (PEI)PEEK (Polyether Ether Ketone)Winner
Max Temperature170°C continuous260°C continuousPEEK
Flame RetardancyUL94 V-0 (inherent)UL94 V-0Ultem
Cost~$40/kg~$100+/kgUltem
Chemical ResistanceGoodExceptionalPEEK
Tensile Strength85 MPa100 MPaPEEK
Smoke/ToxicityExtremely lowLowUltem

Which Material Should You Choose?

Choose Ultem (PEI) when:

  • Aircraft interior components (FAR 25.853)
  • Electrical connectors and insulators
  • Steam-sterilizable medical devices
  • Low smoke/toxicity requirements
  • Semiconductor test sockets
View Details Ultem (PEI)

Choose PEEK (Polyether Ether Ketone) when:

  • Extreme temperature applications (>200°C)
  • Aggressive chemical environments
  • Aerospace structural bearings
  • Oil and gas downhole tools
  • Medical implants
View Details PEEK (Polyether Ether Ketone)

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