PTFE Properties: Mechanical, Thermal & Electrical Data

PTFE (polytetrafluoroethylene) has a property profile unlike any other engineering plastic: the lowest coefficient of friction in the polymer family, near-universal chemical resistance, and continuous-use temperature of 500°F (260°C), paired with unusually low mechanical strength and pronounced cold-flow under sustained load. This page presents quantitative property data for virgin PTFE and the four major filled grades — glass, carbon, bronze, and MoS₂ — drawn from ASTM test methods so you can specify the right grade for your application.

At a Glance

• Tensile strength (virgin): 2,500–4,500 psi — low compared to engineering plastics
• Coefficient of friction: 0.05–0.10 — lowest of any unfilled plastic
• Max continuous temp: 500°F (260°C); decomposes above 620°F (327°C melting, onset of decomposition higher)
• Dielectric constant: 2.1 at 1 MHz — among the lowest of all solid insulators
• Thermal expansion: ~5.5 × 10⁻⁵ in/in/°F — roughly 10× that of steel
• Limiting PV (virgin, unlubricated): ~1,000 psi·ft/min — creep-limited, not thermally limited
• Water absorption: <0.01% — essentially zero moisture uptake

Mechanical Properties

Tensile and Elongation

PTFE is mechanically soft. Tensile strength of virgin material ranges 2,500–4,500 psi depending on molecular weight and processing method — compression-molded billets trend toward the higher end of that range, ram-extruded rod slightly lower. Elongation at break is very high at 200–400%, reflecting the material's ductility before failure. This softness is the primary reason filled grades are used in load-bearing service.

Compressive Creep (Cold Flow)

Cold flow is PTFE's most significant engineering limitation. Under sustained compressive stress — even at room temperature — PTFE deforms plastically without catastrophic failure. A bearing or gasket under 500 psi will dimensionally change over weeks or months of service. Filled grades and spring-energized seal designs mitigate this. Glass-filled PTFE (25%) reduces deformation by roughly 50–60% compared to virgin under identical load and time conditions.

Coefficient of Friction

Virgin PTFE against polished steel produces a static coefficient of friction of 0.05–0.08 and a dynamic coefficient of 0.04–0.10 — values that are essentially self-lubricating without additives. The mechanism is a thin PTFE transfer film that deposits on the mating surface. This transfer film is beneficial in clean-room, food-contact, and pharmaceutical environments where liquid lubricants are prohibited.

Thermal Properties

Temperature Range

PTFE crystallizes at approximately 327°F (164°C) — this is technically its melting point, but because the viscosity remains so high at that temperature it does not flow. Continuous service at 500°F (260°C) is the accepted industry standard. Temperatures above 500°F cause slow molecular-weight degradation. Above approximately 620°F (327°C) PTFE begins emitting perfluoroisobutylene and other decomposition products — adequate ventilation is required when machining near-charred material or when operations approach these temperatures.

Cryogenic Performance

One underappreciated property: PTFE retains flexibility and chemical resistance at cryogenic temperatures down to −460°F (−273°C; near absolute zero). This makes it the seal and insulator material of choice for liquid nitrogen, liquid oxygen, and LNG service — environments that cause most other polymers to become brittle.

Thermal Expansion Considerations

The coefficient of thermal expansion (CTE) of ~55 µin/in/°F is roughly 10× that of steel. A 6-inch PTFE rod that swings 100°F will change length by approximately 0.033 inches. This is critical for close-tolerance fits and housings — design in clearance or use a constrained assembly to prevent binding.

Electrical Properties

PTFE is one of the premier solid electrical insulators. The low dielectric constant (2.1) and loss tangent (<0.0002 at 1 MHz) make it particularly valuable at high frequencies — properties that do not degrade significantly with temperature or moisture, unlike many organic insulating materials.

Chemical Resistance

PTFE's resistance to chemical attack is unmatched by any other thermoplastic. The inertness arises from the C–F bond energy and the helical fluorine sheath around the carbon backbone — reagents cannot reach the polymer chain. The following categories are resisted without degradation:

• Acids: sulfuric, hydrochloric, hydrofluoric, nitric, phosphoric — all concentrations, up to temperature limits
• Bases: sodium hydroxide, potassium hydroxide — all concentrations
• Solvents: acetone, MEK, THF, DMSO, DMF, chlorinated solvents, aromatic hydrocarbons
• Oxidizers: hydrogen peroxide, bleach, ozone, chlorine gas
• Fuels and oils: gasoline, diesel, hydraulic fluids, silicone oils

Known exceptions (PTFE is not resistant):

• Elemental fluorine (F₂) under pressure at elevated temperature
• Chlorine trifluoride (ClF₃)
• Liquid alkali metals (Na, K) at high temperature
• Certain high-energy radiation environments (radiation causes chain scission)

For reference, PVDF / Kynar covers most industrial chemicals but is attacked by amines, ketones above certain concentrations, and fuming sulfuric acid — all of which PTFE handles without issue.

Filled Grade Property Comparison

For full grade selection guidance, visit the PTFE grades page.

Optical and Physical Properties

Property Data Sources and Test Standards

All mechanical values follow ASTM D1457 (PTFE molding and extrusion materials specification) and ASTM D4894/D4895 for granular and fine-powder resins. Electrical data per ASTM D149 (dielectric strength) and D150 (dielectric constant/dissipation factor). Thermal data per ASTM E1356 (DSC melting), ASTM D648 (HDT), and UL 94 (flammability). Values represent typical ranges from multiple commercial-grade materials; your specific lot may vary — request certified test reports for critical applications.

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Frequently asked questions — Ptfe Teflon FAQ