FEP Fluorinated Ethylene Propylene: Transparent Melt-Processable Fluoropolymer
Published: 2026-05-30
Fluorinated ethylene propylene (FEP) is a fully fluorinated melt-processable fluoropolymer—a copolymer of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP). The HFP comonomer introduces -CF₃ side groups that disrupt the PTFE crystal...
Fluorinated ethylene propylene (FEP) is a fully fluorinated melt-processable fluoropolymer—a copolymer of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP). The HFP comonomer introduces -CF₃ side groups that disrupt the PTFE crystal lattice, reducing crystallinity from PTFE's ~90% to FEP's ~50-70% and enabling conventional melt processing while maintaining the fully fluorinated chemistry that provides near-universal chemical resistance. In effect, FEP is the melt-processable version of PTFE—it offers PTFE-level chemical inertness in a form that can be injection molded, extruded, and thermoformed.
FEP is naturally transparent (the reduced crystallinity allows visible light transmission), which is a distinguishing feature among fluoropolymers—PTFE and PFA are opaque white. This transparency makes FEP the material of choice for chemical process sight glasses, laboratory tubing where fluid visibility is required, and molded components for analytical instruments. FEP processes at melt temperatures of 330-370°C with mold temperatures of 150-200°C. Its continuous service temperature of 200°C is lower than PTFE/PFA (260°C) due to the reduced crystallinity, but this is sufficient for most chemical processing and laboratory applications. FEP's main limitation is low mechanical strength (23 MPa tensile, the lowest among engineering fluoropolymers) and susceptibility to stress cracking at elevated temperature under sustained load.
Technical Properties
| Density | 2.15 g/cm³ |
|---|---|
| Tensile Strength | 23 MPa |
| Melting Point | 260 °C |
| Shrinkage Rate | 3.0-5.0% |
| Flexural Modulus | 0.5 GPa |
| Hdt | 55 °C at 1.82 MPa |
| Continuous Service Temp | 200 °C |
Engineering Tool: Shrinkage & Cost Estimator
Calculate part weight, mold cavity dimensions accounting for shrinkage, and material cost — all locally in your browser.
Equivalents & Cross-References
| Equivalent / Alternate | Action |
|---|---|
| Chemours Teflon FEP | |
| Dyneon FEP | |
| Daikin Neoflon FEP |
Frequently Asked Questions
When should I specify FEP over PFA for a fluoropolymer application?
FEP is preferred over PFA when (1) optical transparency is required—FEP is naturally clear, PFA is opaque white; (2) the application temperature is below 200°C, making PFA's 260°C rating unnecessary; (3) cost is a significant factor—FEP is typically 20-30% less expensive than PFA. PFA is preferred when (1) the application requires the full 260°C continuous service temperature; (2) higher mechanical strength at temperature is needed (PFA retains ~15% higher tensile at 200°C than FEP); (3) flex life is critical—FEP has a lower flexural modulus but is more prone to flex cracking over repeated cycling; (4) the application involves permeation-sensitive environments—PFA's lower gas permeability (~50% less than FEP) is critical for ultra-high-purity semiconductor chemical delivery.
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References & Industry Standards
- ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
- UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
- MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
- ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org