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Unfilled PEEK

Unfilled PEEK is a grade of PEEK. It has the lowest strength and highest ductility compared to the other variants of PEEK. The graph bars on the material properties cards below compare unfilled PEEK to: otherwise unclassified thermoplastics (top), all thermoplastics (middle), and the entire database (bottom). A full bar means this is the highest value in the relevant set. A half-full bar means it's 50% of the highest, and so on.

Mechanical Properties

Compressive (Crushing) Strength

120 MPa 17 x 103 psi

Elastic (Young's, Tensile) Modulus

4.0 GPa 0.58 x 106 psi

Elongation at Break

43 %

Flexural Modulus

3.8 GPa 0.55 x 106 psi

Flexural Strength

150 MPa 21 x 103 psi

Impact Strength: Notched Izod

120 J/m 2.2 ft-lb/in

Rockwell R Hardness


Shear Strength

50 MPa 7.3 x 103 psi

Tensile Strength: Ultimate (UTS)

97 MPa 14 x 103 psi

Thermal Properties

Glass Transition Temperature

240 °C 460 °F

Heat Deflection Temperature At 1.82 MPa (264 psi)

160 °C 320 °F

Heat Deflection Temperature At 455 kPa (66 psi)

250 °C 480 °F

Maximum Temperature: Autoignition

600 °C 1100 °F

Maximum Temperature: Decomposition

570 °C 1060 °F

Maximum Temperature: Mechanical

330 °C 630 °F

Melting Onset (Solidus)

340 °C 640 °F

Specific Heat Capacity

1700 J/kg-K 0.41 BTU/lb-°F

Thermal Conductivity

0.25 W/m-K 0.14 BTU/h-ft-°F

Thermal Expansion

52 µm/m-K

Vicat Softening Temperature

250 °C 480 °F

Electrical Properties

Dielectric Constant (Relative Permittivity) At 1 Hz


Dielectric Constant (Relative Permittivity) At 1 MHz


Dielectric Strength (Breakdown Potential)

20 kV/mm 0.78 V/mil

Electrical Dissipation At 1 Hz


Electrical Dissipation At 1 MHz


Electrical Resistivity Order of Magnitude

14 10x Ω-m

Otherwise Unclassified Properties


1.3 g/cm3 82 lb/ft3

Limiting Oxygen Index (LOI)

38 %

Water Absorption After 24 Hours

0.3 %

Water Absorption At Saturation

0.5 %

Common Calculations

Stiffness to Weight: Axial

1.7 points

Stiffness to Weight: Bending

40 points

Strength to Weight: Axial

20 points

Strength to Weight: Bending

36 points

Thermal Diffusivity

0.11 m2/s

Thermal Shock Resistance

34 points

Followup Questions

Further Reading

ASTM F2026: Standard Specification for Polyetheretherketone (PEEK) Polymers for Surgical Implant Applications

SPI Plastics Engineering Handbook of the Society of the Plastics Industry, Inc., 5th ed., Michael L. Berins (editor), 2000

Modern Plastics Handbook, Charles A. Harper (editor), 1999

Plastics Materials, 7th ed., J. A. Brydson, 1999

Advanced Materials in Automotive Engineering, Jason Rowe (editor), 2012