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Polybenzimidazole (PBI)

PBI is a thermoset plastic. It has the highest mechanical heat stability among thermoset plastics. In addition, it has a moderately low density and a fairly high dielectric strength. The graph bars on the material properties cards below compare PBI to other thermoset plastics (top) 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

350 MPa 50 x 103 psi

Elastic (Young's, Tensile) Modulus

5.9 GPa 0.85 x 106 psi

Elongation at Break

3.0 %

Fatigue Strength

56 MPa 8.1 x 103 psi

Flexural Modulus

6.5 GPa 0.95 x 106 psi

Flexural Strength

220 MPa 32 x 103 psi

Impact Strength: Notched Izod

27 J/m 0.5 ft-lb/in

Tensile Strength: Ultimate (UTS)

160 MPa 23 x 103 psi

Thermal Properties

Glass Transition Temperature

410 °C 770 °F

Heat Deflection Temperature At 1.82 MPa (264 psi)

430 °C 810 °F

Maximum Temperature: Decomposition

590 °C 1090 °F

Maximum Temperature: Mechanical

340 °C 640 °F

Specific Heat Capacity

930 J/kg-K 0.22 BTU/lb-°F

Thermal Conductivity

0.41 W/m-K 0.24 BTU/h-ft-°F

Thermal Expansion

23 µm/m-K

Electrical Properties

Dielectric Constant (Relative Permittivity) At 1 Hz


Dielectric Constant (Relative Permittivity) At 1 MHz


Dielectric Strength (Breakdown Potential)

23 kV/mm 0.88 V/mil

Electrical Resistivity Order of Magnitude

13 10x Ω-m

Otherwise Unclassified Properties


1.3 g/cm3 81 lb/ft3

Limiting Oxygen Index (LOI)

58 %

Water Absorption After 24 Hours

0.4 %

Common Calculations

Stiffness to Weight: Axial

2.5 points

Stiffness to Weight: Bending

46 points

Strength to Weight: Axial

34 points

Strength to Weight: Bending

50 points

Thermal Diffusivity

0.34 mm2/s

Thermal Shock Resistance

84 points

Followup Questions

Further Reading

Thermosets: Structure, Properties and Applications, Qipeng Guo (editor), 2012

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

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