Overview: What Is KEL-F?
KEL-F is the trade name originally introduced by 3M (now used generically) for Polychlorotrifluoroethylene (PCTFE), a semi-crystalline fluoropolymer produced by the free-radical polymerization of chlorotrifluoroethylene (CTFE) monomer. It is chemically closely related to PTFE, but the substitution of one fluorine atom per monomer unit with chlorine dramatically changes its performance profile.
Compared to PTFE, KEL-F offers higher rigidity, better compressive strength, superior transparency (in thin sections), and crucially, virtually zero moisture vapor transmission — a property that makes it indispensable in moisture-sensitive applications.
You may also encounter KEL-F under the trade names Neoflon® PCTFE (Daikin) or Aclon® (Honeywell). In all cases, the base chemistry and core properties are essentially identical.
Key Physical and Chemical Properties
KEL-F's performance comes from its unique molecular architecture. The near-total fluorine coverage of the polymer backbone provides the chemical barrier properties associated with fluoropolymers, while the chlorine substituent introduces slight polarity that increases the material's stiffness and reduces its gas permeability to near zero.
| Property | Value / Range | Unit | Note |
|---|---|---|---|
| Density | 2.10 – 2.16 | g/cm³ | High |
| Tensile Strength | 30 – 38 | MPa | At yield |
| Compressive Strength | 55 – 70 | MPa | Superior to PTFE |
| Flexural Modulus | 1,200 – 1,400 | MPa | Rigid vs. PTFE |
| Hardness (Shore D) | 75 – 80 | – | |
| Service Temp. (continuous) | -200 to +200 | °C | Cryogenic ✓ |
| Melting Point | ~211 | °C | |
| Water Absorption (24 hr) | < 0.01 | % | Near zero |
| Moisture Vapor Transmission | ~0.0005 | g·mm/m²·day | Best of any polymer |
| Dielectric Constant (1 MHz) | 2.3 – 2.5 | – | Excellent insulator |
| Oxygen Index (LOI) | > 95% | % | Non-flammable |
| Coefficient of Friction | 0.3 – 0.4 | – | Higher than PTFE |
| Refractive Index | 1.42 | – | Optically clear in film |
Chemical Resistance
KEL-F exhibits exceptional resistance to a broad range of aggressive chemicals, including:
- Strong acids — sulfuric, nitric, hydrochloric, hydrofluoric (all concentrations)
- Strong oxidizers — fuming nitric acid, chlorine trifluoride, liquid oxygen
- Organic solvents — ketones, esters, alcohols, aromatic hydrocarbons
- Halogens — chlorine gas, bromine, fluorine (at ambient temperature)
It is not compatible with highly reactive fluorinating agents at elevated temperatures (e.g., elemental fluorine above 100°C) or molten alkali metals such as sodium. In all other cases, it is among the most chemically inert materials available.
KEL-F / PCTFE has the lowest moisture vapor transmission rate of any commercially available polymer. This makes it uniquely suited to pharmaceutical blister packaging, semiconductor moisture barriers, and cryogenic valve seals — applications where no other plastic material can match its performance.
— Emco Industrial Plastics Technical Team
KEL-F vs. PTFE: Key Differences
Engineers often choose between KEL-F and PTFE. Both are fluoropolymers and both are chemically resistant, but they serve different ends. Understanding when to use each is critical to component performance.
✅ Where KEL-F Wins
- Near-zero moisture permeability
- Higher compressive strength & creep resistance
- Better dimensional stability under load
- Optical clarity (film/thin section)
- Resistance to liquid oxygen / cryogenics
- Harder, stiffer — better for precision machining
⚖️ Where PTFE Wins
- Lower coefficient of friction (lubricity)
- Higher continuous service temperature (260°C)
- Lower material cost
- Wider availability in stock shapes/sizes
- Better chemical resistance at high temps
- Lower density (lighter parts)
As a rule of thumb: choose PTFE for self-lubricated seals, bearings, and general chemical lining; choose KEL-F when moisture barrier performance, cryogenic service, or higher mechanical loads are the primary design drivers.
Applications & Industries
KEL-F's exceptional combination of properties makes it irreplaceable in demanding applications across a range of industries. Below are the most common use cases.
Aerospace & Defense
Valve seats and seals in cryogenic propellant systems (LOX, LH₂); O-ring backups; insulating standoffs in avionics.
Chemical Processing
Sight glasses, pump liners, valve bodies, and gaskets handling fuming acids, halogens, and aggressive oxidizers.
Pharmaceutical
Blister packaging films with best-in-class moisture vapor barriers to extend shelf life of moisture-sensitive drugs.
Semiconductor / Cleanroom
Ultra-pure fluid handling components; moisture barriers in precision instruments; wafer carriers.
Cryogenic Systems
Valve packing, seals, and gaskets for liquid nitrogen, liquid oxygen, and LNG systems down to -200°C.
Electrical / Electronic
High-frequency cable insulation, capacitor dielectrics, and precision insulating components requiring dimensional stability.
Oil & Gas
Downhole seals, packers, and chemical-injection valve components exposed to H₂S, CO₂, and strong brines.
Optics & Photonics
UV-transparent windows and optical components where PTFE's opacity makes it unsuitable.
Machining & Fabrication Guidelines
KEL-F machines to very tight tolerances and is considered one of the more machinable fluoropolymers — significantly easier to work than soft PTFE. Key recommendations:
General Machining Tips
- Use sharp, high-positive-rake tooling (HSS or carbide) to minimize heat generation.
- Avoid aggressive cuts; light passes at moderate speeds produce the best surface finish.
- Allow material to stabilize at room temperature for 24 hours before finish machining critical dimensions.
- No coolant is required for most operations; dry machining is preferred to avoid contamination.
- Thin sections may flex during machining — support carefully in fixturing.
Cutting Parameters (Starting Point)
| Operation | Speed (SFM) | Feed (IPR) | Depth of Cut |
|---|---|---|---|
| Turning (roughing) | 200 – 400 | 0.010 – 0.020 | 0.050 – 0.150" |
| Turning (finishing) | 400 – 600 | 0.003 – 0.008 | 0.005 – 0.030" |
| Milling | 300 – 500 | 0.005 – 0.012 | 0.030 – 0.100" |
| Drilling | 150 – 300 | 0.005 – 0.015 | Full drill dia. |
Bonding & Joining
Like all fluoropolymers, KEL-F has an extremely low surface energy and does not bond with standard adhesives unless the surface is first sodium-etched (chemically etched with sodium naphthalene) or treated with specialized fluoropolymer primers. Mechanical fastening is usually preferred for structural joints.
Available Forms & Stock Shapes from Emco
Emco Industrial Plastics stocks KEL-F/PCTFE in a range of standard shapes for immediate machining. We also work with customers to source custom-extruded or molded forms for high-volume applications.
- Rod: Diameters from 1/4" up to 6" — ideal for turning seals, valve balls, and custom fittings
- Sheet/Plate: Thickness from 1/8" to 2", available in standard 12"×12" and 24"×24" sizes
- Tube/Pipe: Various OD/ID combinations for fluid handling and insulator applications
- Film: Ultra-thin gauge (down to 0.001") for pharmaceutical barrier packaging — available through our distribution network
- Custom Machined Parts: Our in-house machining team can produce finished components to your drawings and tolerances
Regulatory Status & Certifications
KEL-F is frequently specified in regulated industries. Key approvals and compliance notes:
- FDA Compliance: PCTFE compounds meeting 21 CFR 177.1380 are approved for food contact applications.
- USP Class VI: Medical-grade PCTFE is available meeting USP Class VI biocompatibility testing requirements.
- ASTM D7194: Standard specification for PCTFE plastic materials.
- LOX Compatibility: PCTFE is one of the few polymers approved for use in liquid oxygen systems per NASA and ASTM guidelines.
- RoHS / REACH: Standard PCTFE formulations are compliant.
Frequently Asked Questions
Is KEL-F the same as PTFE?
No. Both are fluoropolymers, but they have different chemistries and performance profiles. PTFE (polytetrafluoroethylene) contains only carbon and fluorine. KEL-F/PCTFE also contains chlorine, which gives it higher rigidity, near-zero moisture vapor transmission, and better cryogenic sealing performance, at the cost of lower service temperature ceiling and higher friction.
What is the maximum service temperature of KEL-F?
KEL-F can be used continuously up to approximately 200°C (392°F). Short-term excursions to 210°C are possible. For higher temperatures, PTFE (260°C) or PFA (260°C) are better choices.
Can KEL-F be used in cryogenic applications?
Yes — this is one of KEL-F's strongest attributes. It maintains excellent mechanical integrity and sealing performance down to -200°C (-328°F), making it the preferred seal material in liquid nitrogen, liquid oxygen, and liquid helium systems.
How does KEL-F compare to PVDF (Kynar)?
PVDF is less expensive and easier to process, but is considerably less chemically resistant (especially to strong bases and some solvents) and has higher moisture absorption. KEL-F is the right choice when you need true near-zero permeability and resistance to the most aggressive chemicals.
Does Emco carry KEL-F in stock?
Yes. Emco Industrial Plastics maintains stock of PCTFE rod, sheet, and tube in our distribution centers. Contact our technical sales team for current inventory and lead times on custom cuts or machined components.