PTFE O-Rings (Teflon)
Universal chemical resistance and the widest temperature range of any sealing material — from cryogenic to high-heat static applications.
Overview
PTFE (Polytetrafluoroethylene), widely known by the DuPont trade name Teflon, is a semi-crystalline fluoropolymer rather than an elastomer, but its chemical inertness and temperature range make it an essential sealing material for applications where no elastomer survives. PTFE and Teflon are the same material — Teflon is a registered trademark for PTFE manufactured by Chemours. Resistant to virtually all industrial chemicals — including concentrated sulfuric acid, hydrofluoric acid, strong alkalis, ketones, esters, and oxidising agents — PTFE is the default specification when chemical compatibility is the overriding requirement.
PTFE O-rings — also called Teflon O-rings or Teflon rings — operate from -200°C (liquid nitrogen service) to +260°C, the broadest temperature range of any sealing material. They are FDA 21 CFR §177.1550 compliant and USP Class VI certified, physiologically inert, and self-lubricating, eliminating the need for external lubrication in many applications.
The critical engineering limitation of PTFE is its lack of elasticity. Unlike rubber O-rings that compress and recover elastically, PTFE relies on controlled groove geometry and mechanical compression to maintain contact force. Cold flow (creep) under sustained load is the primary failure mode — over time, PTFE plastically deforms into the groove, reducing contact stress and allowing leakage. Minimize cold flow by: using grooves with tight dimensional tolerances; specifying filled PTFE compounds (glass, carbon, or bronze filler improves creep resistance significantly); and designing for higher groove compression (20–25% for PTFE vs 15–18% for rubber).
Teflon O-rings (PTFE O-rings) are used in static sealing applications only: flange seals, valve seals, fitting seals, and face seals. For dynamic applications requiring PTFE chemical resistance, spring-energized PTFE seals are the correct alternative.
Lead time: 7–15 days standard; 3–5 days for stocked sizes. MOQ: 1 piece. ISO 9001 certified.
PTFE's molecular structure is remarkably simple and the key to its exceptional properties: a linear chain of carbon atoms, each bonded to two fluorine atoms (-CF₂-CF₂-)n. This chain is highly linear with minimal branching, and molecular weights range from 10⁶ to 10⁷ g/mol. The polymer is semi-crystalline with a crystallinity of 50–70% and a melting point of 327°C. The C-F bond energy (485 kJ/mol) is among the highest in organic chemistry, and the fluorine atoms form a helical protective sheath around the carbon backbone that sterically shields it from chemical attack. Cold flow (creep) arises because PTFE lacks the crosslinked network of elastomers — under sustained compressive load, the linear polymer chains slide past one another through crystalline shear and amorphous relaxation. Fillers interrupt this chain slippage: 15% glass fiber reduces cold flow by 40–50%; 25% carbon fiber reduces it by 50–60%; and 60% bronze reduces it by 60–70% while also improving thermal conductivity. However, fillers reduce chemical purity and FDA compliance, so virgin PTFE remains preferred for pharmaceutical and semiconductor applications unless cold flow is the dominant failure mode.
Quantified comparisons with elastomeric O-rings highlight PTFE's unique advantages and limitations. In compression set testing (ASTM D395), rubber O-rings recover elastically after load removal, showing 15–30% permanent deformation depending on material and temperature. PTFE, being a thermoplastic, shows 60–80% 'compression set' at room temperature after 24 hours — but this is not true elastic set; it is permanent plastic deformation that does not recover. This means PTFE groove designs must account for continuous relaxation: a flange bolted with PTFE O-rings will lose 30–50% of its initial bolt load within the first month unless re-torqued. In temperature range, PTFE spans -200°C to +260°C, versus VMQ silicone's -60°C to +200°C — a 160°C advantage at the low end and 60°C at the high end. The coefficient of friction is 0.05–0.10 for PTFE versus 0.3–1.0 for rubber elastomers — PTFE is 3–10× slipperier, eliminating stick-slip in valve actuation and reducing installation torque. In chemical resistance, PTFE is attacked only by molten alkali metals (sodium, potassium, lithium above 300°C) and elemental fluorine gas at elevated temperature — conditions not encountered in normal industrial practice. Every other chemical, including aqua regia, piranha solution, and concentrated hydrofluoric acid, shows negligible effect on PTFE.
A practical selection and design decision tree: if your application is a static flange seal in a chemical reactor handling concentrated sulfuric acid at 180°C, specify virgin PTFE at 80 Shore D equivalent hardness with 22–25% groove compression and plan for bolt re-torque after 30 days of service. If your application is a valve seat seal in a high-pressure (100+ bar) hydrocarbon manifold with moderate chemical exposure, specify 25% glass-filled PTFE for improved creep resistance and compressive strength — verify that the filler does not react with your process fluid. If your application is a cryogenic liquid nitrogen (-196°C) flange, virgin PTFE is the default choice; it remains ductile and does not embrittle like elastomers, though groove compression must be higher (25%) to compensate for thermal contraction. If your application involves any dynamic motion (reciprocating, rotating, or frequent pressure cycling), do not use a PTFE O-ring — specify a spring-energized PTFE seal or an elastomeric seal with chemical-resistant jacket. If FDA or USP Class VI compliance is required, virgin unfilled PTFE is the only acceptable choice among PTFE variants; filled grades require extractables verification.
Storage of PTFE O-rings is the simplest of all sealing materials. PTFE does not age, oxidize, hydrolyze, or degrade under normal storage conditions. It is immune to ozone, UV, and atmospheric pollutants. The recommended shelf life is effectively unlimited — PTFE O-rings stored for 20+ years show no measurable change in properties. Store in clean, dry conditions away from sharp objects that could nick the surface (surface defects act as stress concentrators and accelerate cold flow). PTFE is electrically insulating and can accumulate static charge in dry environments; in explosive atmospheres, ensure grounding during installation. A common but serious design error is specifying PTFE for dynamic sealing because of its chemical resistance — PTFE has no elastic recovery, so in a reciprocating rod application it will cold-flow into surface imperfections and then tear during reverse stroke, causing rapid failure. Another frequent mistake is over-compressing PTFE (>30%) in an attempt to compensate for cold flow; excessive compression actually accelerates creep by increasing the driving stress, and it can extrude PTFE into bolt holes or clearance gaps.
Material Properties
| Temperature Range | -200°C to +260°C (-328°F to +500°F) |
| Hardness | 55–65 Shore D (equivalent to approximately 90–95 Shore A) |
| Tensile Strength | 20–35 MPa (ASTM D412 equivalent) |
| Elongation at Break | 200–400% |
| Coefficient of Friction | 0.05–0.10 (lowest of any solid material — self-lubricating) |
| Specific Gravity | 2.13–2.19 (heaviest common seal material) |
| Chemical Resistance | Virtually universal — only molten alkali metals and elemental fluorine attack PTFE |
| Color | White / natural |
| Compliance | FDA 21 CFR §177.1550, USP Class VI, RoHS, REACH |
Typical Applications
Chemical Processing
Static valve and pump seals handling concentrated acids, alkalis, chlorinated solvents and aggressive oxidising agents where no elastomer is compatible.
Pharmaceutical
FDA-compliant static seals in drug manufacturing, pure steam systems and high-purity fluid handling requiring USP Class VI and full extractables documentation.
Cryogenics
Static seals in liquid nitrogen (-196°C), liquid oxygen and LNG systems where elastomers embrittle and spring-energized seals are over-specified.
Semiconductor
Ultra-high purity static seals in chemical delivery and wet bench equipment handling HF, H₂SO₄, H₂O₂, and mixed aggressive process chemicals.
Food & Beverage
Inert, non-stick static seals in food processing where flavour transfer, chemical reaction with product, or FDA compliance requirements eliminate elastomer options.
Chemical Compatibility Summary
Compatible With
- - Virtually all chemicals
- - Strong oxidizing acids
- - Aromatic and chlorinated solvents
- - Cryogenic fluids
- - Steam and hot water
Incompatible With
- - Molten alkali metals
- - Fluorine gas at high temperatures
- - Chlorine trifluoride
- - Practically none in standard applications
Compare Nearby Materials
FEP Encapsulated
Use this when you need chemical resistance with more elastic recovery.
View FEP EncapsulatedSpring Energized Seals
Best path when PTFE performance is needed in dynamic or cryogenic sealing.
View Spring Energized SealsFurther Reading
PTFE vs FEP Encapsulated
Static chemistry, recovery limits, and where encapsulated designs fit better.
Read articleSpring Energized Seals vs O-Rings
When plain PTFE and standard elastomers stop being enough for motion or vacuum.
Read articleKey Advantages
Universal Chemical Resistance
PTFE is resistant to virtually all industrial chemicals including concentrated sulfuric acid, hydrofluoric acid, strong alkalis, and most organic solvents. Only molten alkali metals and elemental fluorine gas at elevated temperatures attack PTFE — conditions not present in industrial processes.
Extreme Temperature Range
From -200°C in cryogenic service to +260°C in continuous heat — no other standard sealing material covers this range. Maintains useful properties through thermal cycling without embrittlement at cryogenic temperatures.
Self-Lubricating Surface
PTFE has the lowest coefficient of friction of any solid material (0.05–0.10). No external lubrication required — eliminating lubricant compatibility concerns and contamination risk in food, pharmaceutical, and clean-room applications.
FDA and USP Compliant
Virgin PTFE complies with FDA 21 CFR §177.1550 and USP Class VI requirements for pharmaceutical and medical device applications. Full extractables documentation available.
Dimensional Stability and Infinite Shelf Life
PTFE absorbs less than 0.01% water and shows zero swell in virtually all chemicals, maintaining precise dimensions in aggressive media. Unlike elastomers that harden, soften, or crack with age, PTFE does not oxidize, hydrolyze, or degrade during storage — O-rings remain usable indefinitely when protected from mechanical damage. Specific gravity of 2.13–2.19 provides instant field identification: PTFE is the only common seal material that feels noticeably heavy for its size.
Validated Filler Options for Enhanced Mechanical Performance
When cold flow limits virgin PTFE, filled compounds provide engineered solutions: 15–25% glass fiber improves creep resistance by 40–50% and compressive strength by 30–40% while retaining near-universal chemical resistance; 25% carbon fiber improves wear resistance and eliminates static charge buildup; 40–60% bronze provides maximum compressive strength and thermal conductivity for high-pressure heat exchanger seals. Each filler grade is tested for compressive creep (ASTM D621) and compressive strength to validate performance claims.
Frequently Asked Questions - PTFE
Can PTFE O-rings be used in dynamic sealing applications?
Standard PTFE O-rings are not recommended for dynamic applications due to cold flow (creep) under repeated load cycling. The plastic deformation accumulates with each pressure cycle, progressively reducing groove contact stress until the seal leaks. For dynamic service requiring PTFE's chemical resistance, spring-energized PTFE seals (PTFE jacket with metallic spring energizer) are the correct alternative — the spring compensates for cold flow and maintains contact force throughout service life.
What is the difference between virgin PTFE and filled PTFE O-rings?
Virgin PTFE is pure polytetrafluoroethylene: maximum chemical resistance, FDA/USP compliant, but highest cold flow susceptibility. Filled PTFE incorporates inert fillers to improve mechanical properties: glass fiber (15–25%) improves creep resistance and compressive strength while retaining most chemical resistance; carbon (15–25%) improves wear resistance and dry-running capability; bronze (40–60%) provides maximum compressive strength and thermal conductivity for high-pressure applications. Fillers reduce FDA compliance and chemical resistance slightly — verify for your specific application. For chemical processing and pharmaceutical use, virgin PTFE is preferred unless cold flow is the limiting failure mode.
Does PTFE absorb fluids?
No. PTFE has virtually zero fluid absorption — water absorption is less than 0.01% after prolonged immersion. Unlike rubber elastomers that swell in incompatible fluids (changing compression and sealing force), PTFE maintains its dimensions in essentially all chemical environments. This dimensional stability is a key advantage in precision valve seats and face seal applications where seal thickness directly controls compression and sealing load.
How are PTFE O-rings installed differently from rubber O-rings?
PTFE O-rings require tighter groove tolerances than rubber O-rings because they do not stretch elastically to conform to groove geometry. They are typically installed with a mandrel, cone, or PTFE-specific installation tool to avoid kinking or deforming the ring during assembly. Target groove compression for PTFE is 20–25% (versus 15–18% for rubber O-rings) to ensure adequate initial contact stress to overcome cold flow. Groove surface finish should be Ra 0.40–0.80 μm for static PTFE face seals. Contact us for PTFE-specific groove design data for your application.
Are PTFE O-rings suitable for high-pressure applications?
PTFE has limited extrusion resistance compared to hard rubber compounds or filled PTFE — its higher hardness (55–65 Shore D) limits groove conformance, but cold flow at high sustained pressure can allow the seal to extrude into clearance gaps over time. For high-pressure static seals, use filled PTFE compounds (glass or bronze-filled) for improved creep resistance, reduce the diametral clearance gap to minimum practical tolerance, and consider anti-extrusion backup rings for pressures above 100 bar. For dynamic high-pressure chemical sealing, spring-energized PTFE seals with glass-filled or carbon-filled jackets are the engineered solution.
How do I manage cold flow (creep) in PTFE O-ring seals?
Cold flow is PTFE's primary engineering challenge. Mitigation strategies: (1) Use filled PTFE — glass-filled PTFE reduces cold flow by 40–60% versus virgin PTFE; (2) Design for controlled compression — target 20–25% groove compression, not higher; over-compression accelerates cold flow; (3) Minimize sustained pressure differential — PTFE cold flow is accelerated by both mechanical compression and fluid pressure load; (4) Use spring-energized PTFE seals for any dynamic application — the spring compensates for cold flow continuously; (5) Specify tighter groove tolerances to limit the available void into which PTFE can extrude. For critical long-life static seals, periodic re-torque of bolted flanges compensates for cold flow in service.
When should I use a PTFE O-ring versus a spring-energized PTFE seal?
PTFE O-rings are suitable for: static sealing with moderate bolt loads, infrequent disassembly, and media that are too aggressive for elastomers but where pressure is low (< 50 bar). Spring-energized PTFE seals are required when: the application is dynamic (reciprocating rods, valve stems, rotating shafts); system pressure is very low or vacuum (the spring maintains contact when fluid pressure is absent); temperature cycling causes large dimensional changes in the housing that elastically relaxes a static PTFE O-ring; or sealing with spring-energized PTFE is specified by the equipment OEM. The spring-energized seal typically costs 5–15× more than a PTFE O-ring — justify the cost by the service requirement, not as a precaution.
Do PTFE O-rings have aerospace or pharmaceutical certifications?
Virgin PTFE complies with FDA 21 CFR §177.1550 and USP Class VI, making it suitable for pharmaceutical, bioprocessing, and medical device applications. Full extractables documentation including USP physicochemical tests and cytotoxicity reports is available. For aerospace, PTFE is listed on numerous OEM material specifications (Boeing BMS, Airbus AIMS) for fuel system and hydraulic static seals. Filled PTFE grades require case-by-case approval for pharmaceutical and aerospace use because fillers may introduce extractable inorganics. Semiconductor-grade virgin PTFE is available with batch-tested total metals content by ICP-MS for ultra-high-purity chemical delivery systems.
How do you ensure batch consistency for PTFE O-rings?
PTFE batch consistency is controlled at the resin and fabrication stages: (1) Resin qualification — every PTFE powder lot is tested for bulk density, particle size distribution, and standard specific gravity (SSG, ASTM D4894) to confirm molecular weight and crystallinity. (2) Moulding control — sintering temperature (360–380°C) and cooling rate are monitored with calibrated thermocouples; deviation >5°C is rejected. (3) Machined O-ring control — dimensions are verified on CMM or optical comparator to ISO 3601-1 tolerances; surface finish is checked with profilometer (Ra 0.40–0.80 μm target). (4) Mechanical testing — every production lot is tested for tensile strength (20–35 MPa), elongation (200–400%), and specific gravity (2.13–2.19). (5) Filler verification — filled PTFE lots are tested for ash content to confirm filler loading (±2%) and compressive strength (ASTM D695) to validate mechanical reinforcement. Lot-specific CoCs document all parameters.
Can PTFE O-rings from different suppliers be interchanged?
Virgin PTFE is chemically identical regardless of supplier (Chemours Teflon, Daikin Polyflon, 3M Dyneon) because the polymer is a simple linear chain of -CF₂-CF₂- units with no compositional variation. Dimensional interchangeability depends on manufacturing tolerance compliance to AS568 or ISO 3601-1. Filled PTFE, however, varies significantly between suppliers: glass fiber type (E-glass vs S-glass), fiber length, and surface treatment differ; carbon fiber grade and bronze particle size vary. These filler differences affect compressive strength, creep resistance, and chemical compatibility. For critical applications using filled PTFE, request the supplier's material data sheet and compare compressive strength (ASTM D695), creep (ASTM D621), and filler type before switching. For virgin PTFE in standard chemical service, supplier interchangeability is generally acceptable.
Are there color conventions for PTFE O-rings?
Virgin PTFE is naturally white or opaque off-white — this is the standard color and provides immediate visual distinction from black rubber O-rings. Carbon-filled PTFE is black or dark gray; bronze-filled PTFE is metallic brown-gold; glass-filled PTFE is typically white or slightly translucent with visible fiber texture. Because PTFE's specific gravity (2.13–2.19) is dramatically higher than all elastomers, color is secondary for identification — weight and heft are the primary field indicators. Custom pigmented PTFE is generally avoided because pigments can act as nucleating agents affecting crystallinity and mechanical properties, and most pigments are not FDA approved. For applications requiring color coding, use the natural filler color (black = carbon-filled, brown = bronze-filled) as the identifier.
What is the environmental impact and recyclability of PTFE?
PTFE production involves fluorination chemistry that requires careful environmental management. Our suppliers operate with zero liquid discharge and full fluorochemical waste capture. PTFE itself is chemically inert and non-toxic; it does not bioaccumulate or degrade into harmful byproducts in the environment. From a lifecycle perspective, PTFE's extreme durability (decades in corrosive chemical service) eliminates frequent replacements and associated waste. Virgin PTFE is not biodegradable and cannot be remelted like thermoplastics, but post-industrial scrap (machining chips, flash) is reprocessed into lower-grade PTFE products such as bearings, bushings, and non-critical seals. PTFE is REACH and RoHS compliant. We offer recycled-content PTFE compounds with 30–50% post-industrial regrind for non-pharmaceutical applications, reducing virgin material consumption.