Overview
PTFE (polytetrafluoroethylene, branded Teflon) sits in a unique position in the polymer landscape: extreme strengths on a few axes, severe weaknesses on others. What it does well, no other material does as well. What it does poorly, almost anything else does better.
What PTFE does exceptionally:
- Chemical resistance. PTFE is resistant to virtually every commercial chemistry — strong acids (including hot HF), strong bases, solvents, fuels, hot water and steam, oils. The exceptions are exotic (molten alkali metals, fluorine gas, chlorine trifluoride). For chemically aggressive service, PTFE is often the only viable polymer choice.
- Service temperature range. -200°C to +260°C continuous. The widest of any commercial plastic by a substantial margin.
- Coefficient of friction. ~0.05–0.10 — the lowest of any solid material against itself or against polished steel. The basis of PTFE bearing and non-stick applications.
- Electrical insulation. 10¹⁸ Ω·cm volume resistivity, dielectric strength 16–20 kV/mm. PTFE is the reference plastic for high-temperature electrical insulation.
- Flammability. LOI 95% — essentially non-flammable in air, UL94 V-0 inherent without additives.
What PTFE does poorly:
- Mechanical strength. Tensile 10–25 MPa, modulus 0.4–0.55 GPa. PTFE is mechanically among the weakest engineering plastics.
- Creep / cold flow. PTFE deforms permanently under sustained load even at room temperature. This is the #1 design challenge.
- Thermal expansion. CTE 110–160 × 10⁻⁶/°C — extremely high. PTFE fitted to metal moves dramatically across temperature.
- Bondability. Essentially impossible without surface treatment.
- Cost. ~$17/lb stock material, vs $2/lb for UHMW or $3/lb for POM.
The selection logic is simple: use PTFE when chemical, thermal, electrical, or tribological demands exceed what PEEK or PVDF can handle, and when the mechanical demands are modest enough that PTFE’s cold flow is acceptable. Otherwise, less expensive alternatives almost always work.
Manufacturing — PTFE is not melt-processable
Like UHMW, true PTFE cannot be conventionally injection-molded or screw-extruded. Its melt viscosity at sintering temperature (~360°C) is too high for melt flow through gates and runners. Stock shapes are produced by:
- Compression molding — PTFE powder loaded into steel mold, compressed under high pressure, sintered at 360–400°C, cooled slowly to develop crystallinity. The standard process for sheet, rod, and billet stock.
- Ram (paste) extrusion — PTFE powder mixed with lubricant binder, forced through die, sintered (binder burned off). Used for tube and small-section profiles.
- Skiving — PTFE billets are turned on a lathe to peel off thin film/sheet for tape applications.
When a designer specifies “PTFE injection-molded part,” they almost certainly need PFA or FEP instead — modified fluoropolymers with similar chemical resistance and melt-processability. PTFE itself requires fabrication from stock shapes or specialty molding processes.
Cold flow — the #1 PTFE design challenge
PTFE deforms permanently under sustained load even at room temperature. This isn’t degradation; it’s just how the material behaves. A PTFE gasket compressed under bolt load will lose ~20–30% of its preload over weeks as the material flows. A PTFE bushing in continuous service will deform from circular to oval over months.
The design responses:
- Use glass-filled or carbon-filled PTFE for any load-bearing application. The fillers dramatically reduce cold flow at the cost of some chemical resistance and friction.
- Live-load fastened joints. Belleville washers maintain preload as the PTFE flows. Standard practice for PTFE-gasketed flanges in chemical processing.
- Design for the deformed geometry. PTFE seals get designed knowing they’ll flow into their seal groove — the as-installed dimensions matter less than the equilibrium dimensions.
- Avoid sustained high-stress applications. If continuous tensile or compressive loads exceed ~3 MPa, PTFE is probably the wrong choice.
Machining notes
PTFE machines surprisingly well given its softness. Practical recipe:
- Sharp carbide or HSS, positive rake, high relief angles
- Speed: 200–600 SFM
- Feed: 0.005–0.015 in/rev
- Flood coolant — PTFE’s low thermal conductivity traps friction heat
- Workholding: distributed clamping, low pressure, vacuum tables for sheet
The PTFE-specific machining issues:
- Outgassing at the cut. Dry-machined PTFE at high speeds can produce fluorine compounds that are toxic to inhale. Coolant prevents this and the elevated cutting-edge temperature that causes it.
- Workpiece deflection under clamping. PTFE is too soft for aggressive vise pressure — use soft jaws or vacuum holding.
- Surface finish is texture-limited. PTFE’s surface deforms under any contact pressure, so practical finishes are limited to ~16 Ra regardless of tooling.
Bonding is essentially impossible without surface preparation. Sodium naphthalenide etch is the classic preparation — chemically reduces the PTFE surface, allowing adhesives to bond. Plasma activation is the modern alternative. After either, epoxies and cyanoacrylates work well. Without surface prep, PTFE rejects nearly every adhesive.
Variant selection guidance
- Virgin unfilled PTFE — maximum chemical resistance and lowest friction. Cold flow under any load. Use for non-load gaskets, low- friction sliding surfaces, electrical insulation.
- GF15 / GF25 (Glass-Filled) — standard solution to cold flow. Used for compressive seals, valve seats, gaskets under pressure. Maintains FDA compliance.
- CF25 (Carbon-Filled) — highest-load PTFE. Bushings, bearings against hardened steel. Becomes electrically conductive.
- Bronze-Filled (Fluorosint 207 / TFM-2) — hydraulic seals, valve seats requiring thermal conductivity to dissipate frictional heat.
- Related fluoropolymers (PFA, FEP, ECTFE, ETFE) — when melt processability matters more than maximum PTFE properties. PFA is the closest mechanical and chemical match to PTFE while being injection-moldable.
Applications by industry
- Chemical processing — gaskets, seals, valve seats, pump impellers, pipe liners. PTFE is the standard polymer for aggressive chemistry service. Lined steel pipe (PTFE liner inside a steel pressure shell) is the workhorse construction for corrosive service.
- Semiconductor — wafer carriers, fluid handling fittings, high-purity tubing. PTFE’s combination of low extractables and chemical inertness is unmatched for high-purity service.
- Pharmaceutical and biotech — peristaltic pump tubing, valves, vessel liners. Special grades (Algoflon F4-FF, validated medical PTFE) for cGMP applications.
- Food and cookware — non-stick cookware coatings (the public face of PTFE), commercial baking pans, food-processing equipment liners.
- Aerospace — wire and cable insulation (especially high-temperature zones near engines), seal applications, fluid system components. PTFE-insulated wire is the standard for aerospace harness.
- Electrical / electronics — high-temperature insulation, capacitor dielectric, high-frequency cable jacketing. PTFE’s dielectric losses are among the lowest of any plastic.
- Cryogenic — gaskets, seals, and electrical insulation at liquid-nitrogen and liquid-helium temperatures. PTFE remains tough to -200°C, unlike most plastics that embrittle.
- Medical — vascular grafts (ePTFE / Gore-Tex), surgical sutures (PTFE-coated), implant components. PTFE biocompatibility is well- established for many applications.
- Plumbing — joint sealing tape (the ubiquitous “Teflon tape”), pipe thread sealant. Skived PTFE film is the basis of this consumer-grade application.
Failure modes worth designing around
Cold flow is the dominant in-service failure mode (see section above). Always plan for the deformed geometry, not the as-installed geometry, in any load-bearing PTFE application.
Thermal cycling mismatch with metal. CTE of 110–160 × 10⁻⁶/°C is ~10× steel. A PTFE seal installed at room temperature will be loose at -50°C and over-compressed at 200°C. Design with sliding interfaces or expansion accommodation.
Decomposition above 400°C produces toxic fluorine compounds — perfluoroisobutylene (PFIB) and hydrogen fluoride. Critical in:
- Fire scenarios — PTFE-rich assemblies should be evaluated for fire toxicity
- Processing — operators need ventilation for PTFE molding/welding
- Birds — extremely sensitive to PTFE decomposition products; classic “canary in the coal mine” for overheated cookware
Radiation degradation — PTFE has one of the worst radiation tolerances of any plastic. 1 Mrad gamma causes severe chain scission and mechanical loss. Do not use PTFE for gamma-sterilized medical devices, nuclear applications, or aerospace radiation environments. PEEK or PEI are the radiation-tolerant alternatives.
Bonding failure if surface prep is inadequate. The sodium etch or plasma treatment must be done correctly; cleanability of the treated surface degrades over weeks (treat-and-bond promptly).
PFAS environmental concerns — legacy PTFE production used PFOA (perfluorooctanoic acid) as a processing aid. Modern production has been PFOA-free since ~2015, but the broader PFAS regulatory landscape is evolving and could affect future PTFE specification, especially in EU and California jurisdictions. Track regulations for outdoor and consumer applications.