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Fluorinated Ethylene Propylene (FEP)

FEP is a fluoroplastic (fluorine-based thermoplastic). It has a fairly high density among thermoplastics. In addition, it has a fairly high ductility and a very low tensile strength. The graph bars on the material properties cards below compare FEP to: fluoroplastics (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

Elastic (Young's, Tensile) Modulus

0.43 GPa 0.062 x 106 psi

Elongation at Break

300 %

Flexural Modulus

0.6 GPa 0.087 x 106 psi

Flexural Strength

24 MPa 3.5 x 103 psi

Tensile Strength: Ultimate (UTS)

20 MPa 2.9 x 103 psi

Thermal Properties

Glass Transition Temperature

60 °C 140 °F

Heat Deflection Temperature At 1.82 MPa (264 psi)

50 °C 120 °F

Heat Deflection Temperature At 455 kPa (66 psi)

70 °C 160 °F

Maximum Temperature: Autoignition

630 °C 1170 °F

Maximum Temperature: Mechanical

200 °C 390 °F

Melting Onset (Solidus)

260 °C 500 °F

Specific Heat Capacity

1170 J/kg-K 0.28 BTU/lb-°F

Thermal Conductivity

0.22 W/m-K 0.13 BTU/h-ft-°F

Thermal Expansion

95 µm/m-K

Electrical Properties

Dielectric Constant (Relative Permittivity) At 1 Hz


Dielectric Constant (Relative Permittivity) At 1 MHz


Dielectric Strength (Breakdown Potential)

22 kV/mm 0.86 V/mil

Electrical Dissipation At 1 Hz


Electrical Dissipation At 1 MHz


Electrical Resistivity Order of Magnitude

16 10x Ω-m

Otherwise Unclassified Properties


2.1 g/cm3 130 lb/ft3

Limiting Oxygen Index (LOI)

80 %

Refractive Index


Water Absorption After 24 Hours

0.010 %

Common Calculations

Stiffness to Weight: Axial

0.11 points

Stiffness to Weight: Bending

12 points

Strength to Weight: Axial

2.6 points

Strength to Weight: Bending

7.6 points

Thermal Diffusivity

0.088 mm2/s

Thermal Shock Resistance

35 points

Followup Questions

Further Reading

ASTM D2116: Standard Specification for FEP-Fluorocarbon Molding and Extrusion Materials

Fluoroplastics: Volume 2 - Melt Processable Fluoropolymers, Sina Ebnesajjad, 2003

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