PTFE / Teflon FAQ: 10 Common Engineering Questions

These are the questions engineers and procurement teams ask most often when specifying or substituting PTFE. Answers are grounded in material data, not marketing language.

At a Glance

Continuous service limit: 500°F (260°C) — one of the highest among plastics
Chemical resistance: essentially universal, with only a handful of exceptions
Cold flow (creep): the number-one design constraint for mechanical applications
FDA compliance: virgin grade only; filled grades require verification
Lowest friction of any engineering plastic: 0.05–0.10 CoF unfilled
Not injection moldable: processed by compression molding, ram extrusion, or paste extrusion only

Q1: What is the difference between PTFE and Teflon?

Teflon is a registered trademark of Chemours (formerly DuPont) for their brand of PTFE and other fluoropolymer products. PTFE (polytetrafluoroethylene) is the generic chemical name for the polymer. All Teflon is PTFE, but not all PTFE is branded Teflon — many manufacturers produce PTFE resin and stock shapes without the Chemours trademark.

For engineering specification purposes, the correct designator is the ASTM standard (D1457 for resin, D3293/D3295/D3296/D3308 for stock shapes), not a brand name. Specifying "PTFE per ASTM D3295" on a drawing is brand-neutral and procurement-robust.

Q2: What is the maximum temperature PTFE can handle?

The accepted continuous-use temperature for PTFE is 500°F (260°C). Intermittent peaks to 550°F (288°C) are generally tolerable without permanent property loss.

Above 500°F, molecular-weight degradation accelerates. PTFE begins to melt at approximately 327°C (621°F) — but even at its melting point the viscosity remains so high that it cannot be conventionally extruded or injection-molded. Above approximately 260°C, processing fumes can become a health concern; adequate ventilation is required.

At the cold end, PTFE is one of few plastics that remains flexible and functional at cryogenic temperatures — it retains its properties at −460°F (−273°C, near absolute zero), which makes it the standard material for cryogenic seals and LNG service.

Q3: Is PTFE resistant to all chemicals?

Very nearly, but not quite. PTFE resists essentially all acids (including hydrofluoric acid, a notoriously corrosive reagent), all bases, all organic solvents, all oxidizers, and all fuels under normal industrial conditions. The practical exceptions are:

Elemental fluorine (F₂) at high pressure and elevated temperature
Chlorine trifluoride (ClF₃) — an extremely reactive oxidizer
Alkali metals in liquid form (sodium, potassium, cesium) at elevated temperature
High-energy radiation (gamma, electron beam) — causes chain scission and embrittlement

These conditions are essentially never encountered in general chemical processing. For 99%+ of industrial applications, PTFE can be treated as universally chemically resistant. Compare to PVDF / Kynar, which is attacked by amines, ketones above certain concentrations, and fuming sulfuric acid — see the PVDF vs PTFE comparison for details.

Q4: What is cold flow (creep), and how do I design around it?

Cold flow is the tendency of PTFE to deform plastically under sustained compressive or tensile load — even at room temperature, well below the melting point. Unlike metals, which creep only at high fractions of their melting temperature, PTFE creeps at ambient conditions.

Practical consequences:

A PTFE gasket under bolt load will lose thickness over days to weeks, reducing the clamping force on the flange
A PTFE bushing under sustained radial load will deform out-of-round
A PTFE bearing plate will thin unevenly under non-uniform load

Design strategies to mitigate cold flow:

Use filled grades: 25% glass-filled or 60% bronze-filled PTFE creeps significantly less than virgin
Spring-energized seals: use a metal or elastomer spring to maintain sealing pressure as the PTFE creep-deforms
Belleville washers on gasketed flanges: compensate for gasket thinning by maintaining bolt load
Constrained geometry: PTFE in a groove or counterbore that limits extrusion direction (e.g., a dovetail groove for piston packing) performs better than an unconstrained flat seal
Distribute the load: use larger contact areas to reduce unit pressure

Q5: Which PTFE grade should I use for a dynamic seal?

For reciprocating and rotary seals under sustained load, carbon-filled PTFE (15%) provides the best wear life — typically 10–100× longer than virgin PTFE in the same conditions. The carbon filler improves tribological performance without significantly raising friction above virgin levels.

For seals in contact with strong oxidizing acids or HF, carbon-filled PTFE maintains its chemical resistance advantage (unlike glass-filled grades, where the glass fibers are attacked). However, carbon-filled PTFE is electrically conductive, which may matter in certain applications.

For highest compressive strength (high-pressure hydraulic rod seals, for example), bronze-filled PTFE (60%) is the choice — better dimensional stability, higher PV limit, and good heat dissipation.

For FDA-regulated food or pharma applications, virgin PTFE is the default because filled grades generally do not carry 21 CFR 177.1550 status. See the PTFE FDA food-grade guide for details.

Q6: Can PTFE be welded or bonded?

PTFE cannot be welded using conventional hot-gas welding techniques because the melt viscosity remains extremely high even above the melt temperature — the material will not fuse in the same way thermoplastics like PVDF or polyethylene do. PFA, the melt-processable equivalent, can be hot-gas welded.

PTFE can be bonded with adhesives, but not easily. The surface must be chemically etched (using sodium-naphthalene or similar treatments) to create bondable surface chemistry — the fluorine sheath that makes PTFE chemically inert also makes it resistant to standard adhesives. Etching degrades PTFE's surface chemically, which is acceptable for structural bonding but not for chemical process surfaces.

For complex assemblies, the practical approaches are: (1) mechanical fastening of machined PTFE components, (2) press fits or constrained fits using PTFE's thermal expansion, or (3) switch to PFA for components requiring welded joints.

Q7: What tolerances can I hold when machining PTFE?

Routinely achievable: ±0.005 inches on turned dimensions in virgin PTFE with standard carbide tooling. With care — including allowing the part to thermally stabilize before measurement — ±0.002–0.003 inches is achievable.

Filled grades hold tighter tolerances because they have lower thermal expansion and less creep during machining:

25% glass-filled or 15% carbon-filled: ±0.002–0.003 in. routinely; ±0.001 in. with care
60% bronze-filled: ±0.001–0.002 in.

Key tolerancing considerations:

PTFE's CTE (~55 µin/in/°F) is 10× that of steel — parts measured at shop temperature will change dimension in service
Allow 30 minutes of temperature stabilization after machining before measuring
Support thin walls and slender features to prevent deflection during cutting

The PTFE machining guide covers speeds, feeds, and setup in detail.

Q8: Is PTFE food safe? What certification should I look for?

Virgin PTFE is FDA-listed under 21 CFR 177.1550 for repeated food contact across all food types. This covers aqueous, acidic, fatty, and alcoholic food products at temperatures from cryogenic up to the material's continuous-use limit.

What to ask for from your supplier:

Certificate of Conformance (C of C) that specifically cites 21 CFR 177.1550 — not just "food-grade"
If NSF/ANSI 51 is required, request the NSF listing number and verify it against NSF's online database
For dairy/beverage CIP applications, ask about 3-A sanitary standard compliance

Filled grades (glass, carbon, bronze) are not automatically FDA-compliant — the FDA regulation covers PTFE resin, not composite compounds. Carbon-filled and bronze-filled grades are generally not acceptable for food contact. Glass-filled grades require supplier documentation confirming regulatory basis.

Q9: How does PTFE compare to UHMW polyethylene in cost?

UHMW polyethylene is dramatically less expensive — typically 1/5 to 1/10 the cost of PTFE per pound, with sheet and rod readily available from stock at commodity pricing. For many wear-strip, chute-liner, and low-friction bearing applications, UHMW is the cost-rational choice.

However, UHMW cannot substitute for PTFE when:

Service temperature exceeds ~180–200°F (UHMW softens and loses properties)
The chemical environment includes oxidizing acids, halogenated solvents, or aromatic hydrocarbons (UHMW is not resistant to all of these)
The application requires sterilization compatibility (UHMW deforms at autoclave temperatures)
Lowest-possible friction is critical (PTFE CoF is lower than UHMW)

The UHMW vs PTFE Teflon comparison provides a full cost-vs-performance breakdown to guide grade substitution decisions.

Q10: Why can't PTFE be injection molded, and what are my options for complex shapes?

PTFE does not melt into a flowable liquid at any temperature below decomposition. The viscosity at its crystalline melting point (~327°C) is approximately 10¹⁰ Pa·s — so high that no conventional injection molding or screw extrusion system can handle it. This is a fundamental property of the PTFE polymer chain, not a processing limitation that can be engineered around.

Available processing options for complex PTFE geometries:

Compression molding + sintering: the primary method for blocks, rods, and tubes. The pressed billet is then machined to final geometry.
Ram extrusion: for rod and tube of moderate length; lower molecular weight than compression-molded.
Paste extrusion (fine powder): for wire insulation and thin tube; requires lubricated extrusion with subsequent heating to remove the lubricant.
CNC machining from stock: for one-offs and moderate quantities, machining from compression-molded billet is usually the fastest and most economical path to complex shapes.
Switch to PFA: if the geometry requires injection molding (thin walls, complex features, threaded inserts), PFA provides equivalent chemical resistance and is fully melt-processable. Cost is higher, but tooling complexity is lower for complex parts.

For design-for-machinability guidance, see machining PTFE.

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Frequently asked questions — Ptfe Teflon FAQ