PTFE (Teflon)
Also: Teflon, polytetrafluoroethylene, virgin PTFE, mechanical-grade PTFE, glass-filled PTFE, carbon-filled PTFE, bronze-filled PTFE, Rulon (filled PTFE compounds), Fluon, Polyflon, modified PTFE (TFM), expanded PTFE (ePTFE), PFA / FEP (melt-processable relatives)
PTFE (Teflon): the most inert, slipperiest plastic, usable from cryogenic to 260 °C. Soft and weak; it cold flows under load, so bearings use filled grades.
Sourcing PTFE parts or stock?
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At a glance
| Density | 2.16 g/cm³ (0.078 lb/in³) |
|---|---|
| Tensile strength | 20-35 MPa (2.9-5.0 ksi) at break |
| Yield strength | About 9-12 MPa (1.3-1.7 ksi); it creeps at stresses well below this, so design from creep and deformation-under-load data |
| Hardness | Shore D 50-60 |
| Elongation | 250-400% at break |
| Modulus of elasticity | 0.4-0.6 GPa (0.06-0.09 Msi) tensile |
| Thermal | Melts at 327 °C (621 °F) but does not flow; continuous service 260 °C (500 °F); usable to about -200 °C (-328 °F); crystal transitions near 19 °C and 30 °C (66 and 86 °F) change its volume about 1%; HDT only about 50-55 °C (120-130 °F) at 1.82 MPa |
| Composition | Polytetrafluoroethylene, (C2F4)n; virgin, or filled with 15-25% glass fiber, carbon, graphite, 40-60% bronze, or MoS2 for bearing and seal service |
Typical values, Virgin (unfilled) compression-molded and sintered sheet and rod, 23 °C (73 °F). Confirm against the mill certificate and the purchase spec.
- MachinabilityGood
- Cuts very easily with sharp, polished, high-rake tools, but it is soft, deflects and creeps under clamps. Hold ±0.05 mm (±0.002") only with temperature control, because the 19 °C transition moves size. Filled grades wear tools. No smoking where PTFE chips are made.
- WeldabilityPoor
- Cannot be solvent bonded, and nothing sticks to it untreated. Adhesive bonding needs a sodium-naphthalene etched or plasma-treated surface, sold as "etched PTFE". Fusion welding is specialist lining work; capture, clamp or fasten parts instead.
- FormabilityPoor
- Not thermoformed or bent in practice. Parts are machined from molded or ram-extruded shapes, paste extruded as tube and wire insulation, or cut from skived sheet and film.
- Corrosion resistanceExcellent
- Essentially inert: resists all common acids, bases, oxidizers and solvents up to 260 °C (500 °F); only molten alkali metals, fluorine and a few fluorinating agents attack it. Absorbs under 0.01% water and is unaffected by sunlight. Filled grades inherit the filler limits: glass is attacked by hydrofluoric acid and strong alkali.
PTFE (polytetrafluoroethylene, best known as Teflon) is a fully fluorinated polymer. Its carbon-fluorine bonds make it almost completely inert: only molten alkali metals, elemental fluorine and a few fluorinating agents attack it. It has the lowest coefficient of friction of any solid (about 0.05-0.10 against polished steel), absorbs no water, sticks to nothing, is an outstanding high-frequency insulator (dielectric constant about 2.1), and works continuously from cryogenic temperatures to 260 °C (500 °F).
Mechanically it is weak and soft: about 20-35 MPa (3-5 ksi) tensile, a modulus near 0.5 GPa and Shore D 50-60. Its defining problem is creep, called cold flow: under a steady load, even at room temperature, it keeps deforming, so a PTFE gasket loses bolt load, a seat extrudes out of its groove and a press fit loosens. Fillers are the fix. Glass fiber (15-25%) improves creep and wear, carbon and graphite add stiffness and suit water service, and bronze (40-60%) gives the best creep resistance and thermal conductivity. Filled compounds (Rulon is one family) cut wear by orders of magnitude but give up some chemical and electrical purity.
PTFE cannot be melt-processed. Its melt is so viscous that it is shaped almost like a ceramic: powder is pressed into a preform, sintered above its 327 °C (621 °F) melting point, then machined; or it is ram extruded and paste extruded into rod, tube and wire insulation. For molded parts, use the melt-processable fluoropolymers PFA or FEP. Keep PTFE away from lasers, torches and overheated tooling: above about 350 °C (660 °F) it begins to decompose into toxic fluorinated gases.
Heat treatment
Not heat treated for properties; shapes are sintered by the producer. Precision parts are often stress relieved between roughing and finishing by heating slowly to a temperature above the part service temperature (commonly 150-260 °C, 300-500 °F), holding, and cooling slowly. Measure finished parts at a stated temperature, usually 23 °C (73 °F).
Tempers and conditions
- Virgin (white)
- Mechanical or reprocessed grade
- Glass-filled 15-25%
- Carbon- and graphite-filled
- Bronze-filled 40-60%
- MoS2-filled
- Modified PTFE (TFM, lower creep and porosity)
- Etched (bondable) sheet and tape
- Expanded PTFE (ePTFE) gasket tape
Stock forms
- Molded rod, tube and sheet
- Ram-extruded rod
- Skived sheet, film and tape
- Paste-extruded tubing and wire insulation
- Molded billets for machining
- Gaskets and ePTFE joint sealant
Relative cost
Tier 3 of 5. Roughly 2-4x acetal per pound for virgin stock, and at 2.2 g/cm3 a part takes about 50% more material by weight than the same part in acetal. Filled and modified grades cost more.
Typical applications
- Seals, seats, backup rings and piston rings
- Valve seats and diaphragms in chemical service
- Gaskets and flange seals (often ePTFE or filled)
- Slide bearings and bridge bearing pads
- RF connector insulators and cable dielectric
- Chemical-resistant liners, lab ware and pump parts
- Non-stick surfaces in food and packaging machines
Process compatibility
How PTFE takes each process, and what to specify. Each process links to its own guide and to the shops that do it.
| Process | Rating | Notes |
|---|---|---|
| CNC Machining | GoodGood | How most PTFE parts are made: easy cutting, hard size control. Allow for creep and the 19 °C transition in tight fits. Can PTFE (Teflon) be machined? |
| CNC Turning | ExcellentExcellent | Seals, seats, rings and bushings from molded rod or tube; sharp, polished tooling gives a fine finish. |
| CNC Milling | GoodGood | Soft and slippery to hold; use vacuum or light fixturing and sharp cutters, and support thin walls. |
| Swiss Machining | GoodGood | Small insulators and seal components from extruded rod; filled grades wear tools faster. |
| Waterjet Cutting | GoodGood | A clean, cold way to cut gaskets and profiles from sheet; die cutting takes over for thin gaskets at volume. |
| Laser Cutting | Not recommendedNot recommended | Heating PTFE releases toxic fluorinated gases, including hydrogen fluoride; laser shops refuse it. Waterjet, die cut or machine. |
| Injection Molding | Not recommendedNot recommended | PTFE does not melt-flow and cannot be injection molded; parts are compression molded, sintered and machined. Mold PFA or FEP for a molded fluoropolymer. |
| Vibratory Finishing | FairFair | Removes the fuzzy burrs PTFE leaves on small parts; cryogenic deburring is used for complex seals. |
| Bead Blasting | PoorPoor | Too soft: media embeds in the surface. Keep it off sealing and bearing faces. |
Design and sourcing tips
- Name the grade: "virgin PTFE" for chemical, electrical and food service; "25% glass-filled PTFE" or "bronze-filled PTFE" for seals and bearings under load. Unfilled PTFE creeps and wears quickly.
- Capture seals and seats on all sides and let metal carry the load. A free PTFE gasket or seat cold flows and loses preload; spring-energized seals and retorquing compensate.
- State the measuring temperature on tight tolerances: PTFE passes through crystal transitions near 19 °C and 30 °C (66 and 86 °F), so a part measured in a cold shop and a warm lab can differ by several tenths of a percent.
- Allow for thermal expansion of about 100-150 um/m·K, among the highest of any plastic and higher still above room temperature.
- For bonded linings or labels, specify etched PTFE; untreated PTFE holds no adhesive.
- If you need a molded or welded fluoropolymer part, specify PFA or FEP rather than PTFE.
Frequently asked questions
- Is PTFE the same as Teflon?
- Teflon is the Chemours brand name for PTFE, and also for related fluoropolymers such as PFA and FEP. Other producers sell PTFE under their own names, such as Fluon and Polyflon. For a machined part, "PTFE" on the drawing is the right callout; name a brand only if the resin must be traceable to it.
- What is cold flow in PTFE?
- Cold flow is creep at room temperature: under a constant load, PTFE keeps deforming slowly and does not fully recover. Gaskets lose bolt load, seats extrude into clearances and press fits relax. Fillers such as glass, carbon and bronze reduce it several-fold, and good design captures the PTFE so it has nowhere to flow.
- Can PTFE be glued?
- Only after surface treatment. Untreated PTFE has very low surface energy and nothing bonds to it. Sodium-naphthalene etching or plasma treatment makes a bondable surface (brown after etching) that takes epoxy and other structural adhesives. Etched PTFE sheet and tape are sold ready to bond.
- What temperature can PTFE handle?
- Continuous service to about 260 °C (500 °F), and down to about -200 °C (-328 °F). It melts at 327 °C (621 °F) but does not flow. Its load-carrying ability falls well before 260 °C because it creeps, so hot seals and bearings use filled grades or PEEK.
- Can PTFE be injection molded?
- No. PTFE melts at 327 °C (621 °F), but its melt is far too viscous to flow through a gate. Parts are compression molded and sintered, ram extruded or paste extruded, then machined. PFA and FEP are melt-processable fluoropolymers with similar chemical resistance that can be injection molded, at a higher price.
Related materials
Where to verify these values
- Chemours Teflon PTFE resin and fabrication data
- AGC Fluon and Daikin Polyflon PTFE data sheets
- Saint-Gobain Rulon filled-PTFE compound data
- ASTM D4894, D3294 and D1710; ASTM D2990 (creep) test method
