PTFE (Teflon) FAQ — Properties, Grades, Machining & Uses

PTFE (polytetrafluoroethylene), widely known by the DuPont trade name Teflon, is the benchmark fluoropolymer for extreme chemical resistance, high-temperature service to 500°F, and lowest-available coefficient of friction among solid plastics. It is also unique in how it is produced — PTFE cannot be melt-processed and is instead compacted and sintered, giving it distinct handling characteristics. This FAQ addresses the questions engineers and buyers ask most often when specifying PTFE sheet, rod, tube, and filled grades.

What is the difference between PTFE and PFA?

Both PTFE and PFA are fully fluorinated polymers with near-identical chemical resistance and non-stick surfaces. The key differences are:

The critical practical difference is that PFA can be melt-extruded and injection molded, allowing more complex part geometries and tighter dimensional tolerances. PTFE must be sintered from powder and is typically skived (for film) or machined from billets. PFA's transparency allows visual inspection of fluid flow in process equipment. PTFE is preferred for most cost-sensitive applications; PFA is specified when transparency, complex geometry, or certain purity levels are required. See the PTFE vs. PFA comparison for a full evaluation.

What filled PTFE grades are available, and what do they offer?

Unfilled (virgin) PTFE has excellent electrical and chemical properties but suffers from significant cold flow (creep) under sustained load, limiting its use as a bearing or structural material. Fillers address this by reinforcing the PTFE matrix:

Glass-filled PTFE (15–25% glass fiber):

• Significantly improved creep resistance and dimensional stability
• Increased compressive strength and wear resistance
• Slightly reduced chemical resistance (avoid HF and strong alkalis with glass-filled)
• Standard bearing and seal grade for general industrial use

Carbon-filled PTFE (15–25% carbon or graphite):

• Excellent dry-running bearing performance; lower friction than glass-filled
• Good thermal conductivity — dissipates frictional heat effectively
• Electrically conductive (use where antistatic properties are needed; avoid where electrical insulation is required)
• Best for piston rings, valve seats, and dry-running bearing surfaces

Bronze-filled PTFE (40–60% bronze):

• Highest load capacity of any PTFE-filled grade
• Best thermal conductivity for heat dissipation in loaded bearings
• Good wear resistance under high PV (pressure × velocity) conditions
• Used for heavy-duty piston and rod seals, large valve seats
• Not suitable for food contact or applications where bronze contamination is prohibited

MoS₂-filled PTFE (2–5% molybdenum disulfide):

• Further reduced friction coefficient vs. unfilled PTFE (one of the lowest sliding friction values available)
• Good wear performance in low-speed, high-load applications
• Not suitable for oxidizing environments (MoS₂ oxidizes above ~600°F)

See the PTFE grades guide for tabulated property data on all filled grades.

What is cold flow (creep) in PTFE, and how do I account for it?

Cold flow (also called creep) is the tendency of PTFE to deform slowly under sustained compressive or tensile load, even at room temperature, without reaching the yield point. This occurs because PTFE's crystalline structure allows molecular chains to rearrange under stress over time. Practical implications:

• Gaskets: PTFE gaskets will creep under bolt load, reducing seating stress over time. Specify a load-bearing PTFE sheet (expanded PTFE or glass-filled PTFE) or use a spring-loaded retorque procedure.
• Bearings: Unfilled PTFE under sustained radial load will deform. Use glass-filled, carbon-filled, or bronze-filled PTFE for bearing applications.
• Structural applications: PTFE should not carry sustained tensile or compressive structural loads without accounting for long-term deformation. Thick PTFE spacers under bolt tension require regular inspection.

Filled grades reduce creep substantially. For critical sealing applications, expanded PTFE (ePTFE) sheet or envelope gasket forms are often preferred over solid PTFE. Review PTFE properties and creep data for quantitative deformation rates.

How do you machine PTFE?

PTFE machines readily on standard CNC equipment, but its unique properties require specific techniques:

• Tooling: Sharp HSS is adequate for short runs; carbide recommended for production. PTFE's low strength means tooling wear is low, but dull tools cause smearing rather than clean cuts.
• Turning: 300–600 SFM; positive rake angles (10–15°); light feed. PTFE is soft and gummy — aggressive cuts push the material rather than cut it cleanly.
• Milling and drilling: Standard end mills and twist drills work. Avoid dwelling in a cut — PTFE conducts heat poorly and localized heat buildup causes smearing.
• Coolant: Dry machining or light air blast is preferred. Water-based coolant can be used but is generally unnecessary.
• Tolerances: PTFE has a high CTE (5.5 × 10⁻⁵ in/in/°F) and significant anisotropy in extruded rod. Allow material to stabilize at machining temperature. Tight tolerances (± 0.001–0.002") require careful thermal management.
• Clamping: PTFE deforms under clamping pressure. Use soft jaws or nesting fixtures; avoid excessive clamping force.
• Part stability: Skived PTFE film is not dimensionally stable for machining. Machine from compression-molded billet for tight-tolerance parts.

Full parameters are in the PTFE machining guide.

What is the 500°F continuous-service rating of PTFE?

PTFE can be used continuously at 500°F (260°C) without significant degradation of mechanical or chemical properties. This is the highest continuous-service temperature of any standard engineering plastic stock shape. Above 500°F, PTFE begins to release trace fluorocarbon gases; above its decomposition temperature of ~572°F (300°C), it releases toxic perfluoroisobutylene (PFIB) and other fluorocarbon gases. Machining operations that generate excessive heat or burning PTFE dust should be conducted with ventilation. The melting point of PTFE is approximately 620°F (327°C), but it does not melt in the conventional sense — it transitions from crystalline to amorphous gel rather than flowing as a liquid. For comparison, PVDF is rated to 280°F and polypropylene to 220°F continuous.

What is the non-stick mechanism of PTFE?

PTFE's non-stick character derives from its molecular structure. The fluorine atoms surrounding the carbon backbone create a surface with an extremely low surface energy — approximately 18–20 mN/m, one of the lowest of any solid material. A liquid or adhesive requires surface energy higher than the substrate to wet and adhere; most materials have surface energies of 30–70 mN/m. Because PTFE's surface energy is below the critical wetting threshold for nearly all liquids, adhesion is minimal. The same property means PTFE surfaces are extremely difficult to bond to — standard adhesives do not adhere without chemical or plasma surface etching (sodium naphthalene etch, plasma treatment). This is why PTFE-lined components are mechanically retained rather than adhesively bonded. See PTFE applications for how this non-stick property is exploited in process equipment.

What is skived PTFE film?

Skived PTFE film is produced by rotating a large sintered PTFE billet against a sharp blade, peeling off a continuous thin sheet in a process analogous to peeling a log into veneer. Skived film is available in thicknesses from 0.001" (0.025 mm) to 0.060" (1.5 mm), in widths of 12"–60" and continuous roll lengths. Skived PTFE film is used for:

• Electrical insulation tape (PTFE tape for wire and cable wrap)
• Non-stick release surfaces in composite molding (peel ply, release film)
• Diaphragms and seals in pumps and valves
• Flexible liner for chemical hose and tubing

Note that skived film is not dimensionally stable and should not be used for close-tolerance machined components — use compression-molded billet PTFE for those applications. PTFE tape (thread sealant tape, commonly called Teflon tape) is a distinct product: a stretched and oriented skived PTFE film sold in narrow rolls for pipe thread sealing. See PTFE specifications for film thickness ranges.

What is PTFE tape used for?

"PTFE tape" commonly refers to two distinct products:

1. Thread sealant tape (plumber's tape): Thin, white PTFE film wound onto small rolls, applied to pipe threads to provide a chemical-resistant, pressure-tight seal without pipe dope. Used in water, air, chemical, and gas lines. The soft, deformable film conforms to thread geometry and fills gaps without hardening. Not appropriate for sealing large-gap joints or flange faces.

2. PTFE self-adhesive film tape: A wider, thicker skived PTFE film with a pressure-sensitive adhesive backing, used to create non-stick or low-friction surfaces on tooling, guides, conveyor components, and mold surfaces. Available in widths from 0.5" to 24" and thicknesses of 0.003"–0.020".

Both are derived from the same base PTFE resin and share its chemical resistance and temperature ratings. For chemical-process sealing, use only the thread-seal or ring-gasket form appropriate for your joint geometry. See PTFE applications for gasket and sealing applications.

What sizes does PTFE sheet and rod stock come in?

Standard stocked forms for PTFE:

• Sheet: 0.031" to 4.0" thick, in 12"×12", 24"×24", and 24"×48" cut sizes (PTFE sheet is press-molded in pads rather than extruded in large panels, so sheet sizes are more limited than thermoplastics)
• Rod: 0.125" to 12.0" diameter, lengths typically 12"–48"
• Tube: Various OD/ID combinations; extruded PTFE tube is available from small fractions to several inches OD
• Skived film/roll: 0.001"–0.060" thick, 12"–60" wide, continuous roll

Virgin (unfilled) PTFE is the most widely stocked. Glass-filled and carbon-filled grades are widely available; bronze-filled is common for bearing applications. For complete stocked sizes, see PTFE specifications.

Is PTFE FDA compliant?

Virgin (unfilled) PTFE complies with FDA 21 CFR 177.1550 for food-contact applications. PTFE is also listed in:

• USP Class VI — pharmaceutical and medical device applications
• NSF/ANSI 51 and 61 — food and drinking water equipment
• 3A Sanitary Standards — dairy and beverage equipment

Filled grades have variable FDA status:

• Glass-filled PTFE: Generally FDA-compliant (glass fiber listed in 21 CFR 177.1550)
• Carbon-filled PTFE: Graphite-filled grades generally compliant; some carbon black sources are not listed
• Bronze-filled PTFE: Not FDA-compliant for direct food contact; bronze may contaminate food
• MoS₂-filled PTFE: Not recommended for food contact; MoS₂ is not FDA-listed

Always obtain a compliance letter from the manufacturer confirming the specific filled grade's FDA status. See PTFE FDA guide for documentation details.

How does PTFE cost compare to other fluoropolymers?

PTFE is the lowest-cost fluoropolymer per pound in rod and sheet stock form, reflecting its high production volume and relatively mature manufacturing process:

Note that PVDF is less expensive than PTFE per pound despite being a lower-performance material overall — this reflects PVDF's melt-processability (lower manufacturing cost per unit) vs. PTFE's sintering process. When PTFE's temperature or chemical resistance is genuinely required, there is no cost-effective substitute. When it is not, PVDF often delivers sufficient performance at lower cost. See the PTFE vs. PVDF comparison.

What is the dielectric constant and electrical behavior of PTFE?

PTFE is the gold standard for low-loss electrical insulation:

• Dielectric constant: 2.1 (essentially constant from DC to GHz frequencies)
• Dissipation factor: < 0.0002 at 1 MHz — one of the lowest of any solid dielectric
• Dielectric strength: 480–560 V/mil
• Volume resistivity: > 10¹⁸ Ω·cm

These properties make PTFE the preferred substrate for high-frequency microwave laminates, coaxial cable insulation, and RF connectors. The dielectric constant of 2.1 is stable over a wide temperature range (-100°F to +500°F), which is critical for signal-integrity applications. For comparison, G10 and FR4 has a dielectric constant of 4.3–4.8 at 1 MHz, causing significantly higher signal attenuation at high frequencies. See PTFE electrical properties for frequency-dependent data.

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Frequently asked questions — Ptfe Teflon FAQ