Viton® Extreme ETP O-Rings

Viton® Extreme ETP exists to solve one specific problem: standard Viton® (FKM) is not chemically tough enough for your fluid, but FFKM costs more than the job can justify. ETP is the compound in the gap. It is a specialty FKM built as an ethylene / tetrafluoroethylene (TFE) / perfluoromethylvinyl ether (PMVE) terpolymer, and the ethylene in that backbone is the whole point. It closes the exact holes in standard FKM’s chemical resistance without giving up the acid, fuel, and hydrocarbon resistance that made FKM worth buying in the first place.

Standard fluororubber is made by polymerizing vinylidene fluoride (VDF) with monomers such as hexafluoropropylene (HFP), TFE, and PMVE, landing at a fluorine content of roughly 65 to 71 percent. That chemistry is superb against oils, fuels, and acids, and it has two well-documented weak points: amines have a destructive effect on it, and its vulcanizates swell strongly in ketones and esters. Every engineer who has pulled a mushy, swollen Viton® O-Ring out of an MEK line knows the failure by heart.

ETP was built to close that gap. That is the pitch, and it is an honest one: broader chemistry than FKM at a fraction of FFKM’s price. For a lot of jobs it is a genuine FFKM alternative. For a few, it is not. This page covers both.

Quick specs

Common names

Purchasing, engineering, and the drawing rarely agree on what to call this material. All of these mean the same thing:

• Viton® Extreme ETP, the full Chemours designation
• Viton® ETP or just ETP, the shop-floor short form
• ETP-600S and similar, the base polymer grade names
• Ethylene-based FKM or ethylene FKM, the generic description
• FKM, the ASTM D1418 class it falls under, which is why the drawing alone often will not tell you whether standard or ETP was intended

Mechanical properties

• Very good high-temperature capability, with a ceiling above standard FKM
• Good compression set resistance at elevated temperature
• Good tensile strength and tear resistance for a highly fluorinated elastomer
• Excellent resistance to swell in polar solvents, which is the property that separates it from ordinary FKM
• Good resistance to oxidation, ozone, weather, and sunlight
• Poor low-temperature flexibility, similar to or slightly worse than standard FKM
• Standard 75 Shore A hardness across the commercial range

The mechanical story here is unremarkable on purpose. ETP is not bought for strength or for dynamic performance; it is bought for chemistry. It behaves roughly like a good FKM in the gland, and it survives fluids that a good FKM does not.

Limitations

The honest list. ETP is a bridge compound, not a miracle:

• Poor low-temperature flexibility. It is stiff below roughly freezing. Cold service is not its game, and no amount of gland design fixes a seal that has gone glassy.
• Expensive versus standard FKM. Far cheaper than FFKM, but a real step up in cost from ordinary Viton®.
• Narrow availability. Fewer sizes, fewer durometers, longer lead times. Much of it is quoted to order rather than pulled off a shelf.
• Not a universal seal. For the very worst chemistry combined with the highest heat, FFKM still wins, and it is not close.
• For hot water, steam, and amines specifically, compare Aflas®. It handles that trio well and often costs less than ETP.
• If standard FKM already covers your fluid, buy standard FKM. We will say that plainly rather than sell you the upgrade. ETP earns its price only when the chemistry actually demands it.

Chemical compatibility

Handles well:

• Strong bases and caustics, including sodium hydroxide and potassium hydroxide service
• Amines, the media that destroy standard FKM
• Ketones such as MEK and acetone, where standard FKM swells badly
• Esters and aldehydes, the other classic FKM failure category
• Alcohols, including methanol and ethanol
• Strong acids, including oxidizing acids, inherited from the FKM family
• Petroleum oils, greases, fuels, and aliphatic and aromatic hydrocarbons
• Chlorinated solvents
• Steam and hot water better than standard FKM, though Aflas® is the specialist there
• Ozone, weather, and sunlight

Attacks it:

• Hot fluorinated solvents and some fluorinated refrigerants
• Molten or gaseous alkali metals
• A short list of exotic media where only FFKM survives

The selling point is breadth, not any single hero result. ETP covers both ends of the pH scale and the polar solvents at the same time. That combination is rare, and it is exactly why ETP shows up in mixed-chemistry plants where one seal has to see acid on Monday and caustic on Thursday. Standard FKM handles the acid and dies on the caustic. EPDM handles the caustic and dies on the hydrocarbons. ETP takes both.

Confirm your exact fluid on the Chemical Compatibility page or in the interactive Chemical Compatibility Chart.

A word on temperature ranges

Our published range for ETP is -8°F to +482°F (-22°C to +250°C). Both ends deserve explanation, because they pull in opposite directions.

• The top end is genuinely high. +482°F sits above standard FKM’s usual +400°F ceiling. If your job is hot and chemically nasty at the same time, that headroom is real and it is part of what you are paying for.
• The cold end is the weakness. ETP is stiff below roughly freezing. It is a high-temperature, broad-chemistry compound that happens to be poor in the cold, and that is the trade the chemistry makes.
• For context, general FKM guidance puts standard types near -4°F, with special low-temperature grades reaching to about -40°F. ETP’s -8°F is right in that neighborhood, and there is no ETP low-temperature grade to escape to. That is why the cold figure looks the way it does.

Any published range assumes the compound, the media, the pressure, the hardware, and the duty cycle all cooperate. Heat plus an aggressive fluid shortens life faster than heat alone. If your application sits near an edge, send us the conditions and we will pull the datasheet for the actual compound rather than guess from a chart.

Shop Viton® Extreme ETP O-Rings

Every Viton® Extreme ETP variation we stock, by size:

Inch (AS568):

• Viton® FKM 75 Duro ETP (Extreme Chemical Resistant)

Metric:

• Viton® Extreme ETP Metric

Need a size or durometer that is not listed? Ask us. Most of the ETP world is made to order, and we quote it regularly.

Variations and grades explained

ETP terpolymer versus standard FKM

The difference is in the monomers. Standard Viton® (FKM) is a VDF-based copolymer or terpolymer, typically VDF with HFP and sometimes TFE. ETP replaces that architecture with ethylene, TFE, and PMVE. The ethylene units change how the polymer responds to polar solvents and to base attack, which is why ETP survives amines, ketones, and caustic while a VDF-based FKM does not. It is not a compounding tweak. It is a different polymer wearing the same ASTM class.

The wider specialty FKM family

ETP is one branch of a family of purpose-built fluoroelastomers. The other well-known branch solves the opposite problem: GLT and GFLT low-temperature types trade some chemical breadth for cold flexibility that standard FKM cannot reach. If cold is your constraint rather than chemistry, those are the grades to ask about, not ETP. See the Viton® (FKM) page and the mil-spec reference for how those types are called out.

By hardness (durometer)

75 Shore A is the standard, and in practice it is close to the only option in stock. It is a sensible default: hard enough to resist extrusion through the gland gap at moderate pressure, soft enough to seal well. Other durometers exist but are quoted to order.

Brand versus generic

Viton® is a registered trademark of The Chemours Company, and Viton® Extreme ETP is their specialty product line. Other producers offer equivalent ethylene-based fluoroelastomer chemistries under their own names. If your drawing says Viton® ETP, tell us whether you need the Chemours polymer specifically or whether an equivalent is acceptable. It sometimes changes both price and lead time.

Where it sits between FKM and FFKM

• Standard FKM: oils, fuels, acids, heat to about +400°F. Dies on amines, ketones, esters, and strong bases. The cheapest of the three by a wide margin.
• Viton® Extreme ETP: everything FKM does, plus the bases, amines, ketones, esters, and alcohols. Heat to +482°F. Poor in the cold. Costs meaningfully more than FKM.
• FFKM: the broadest chemical resistance available and the highest heat. Also the most expensive elastomer on the shelf, often by an order of magnitude.

Read that list top to bottom and stop at the first line that covers your fluid. That is the right compound.

Standards and specifications

Viton® Extreme ETP O-Rings are supplied in AS568 inch sizes and common metric sizes. Useful callouts:

• ASTM D1418: designates the polymer as FKM. ETP is a specialty FKM, not its own ASTM class, so the designation alone does not distinguish it from ordinary Viton®. This trips people up constantly.
• ASTM D2000 / SAE J200: the line-callout system most commercial fluoroelastomer is bought to.
• No dedicated military O-Ring spec exists for ETP. The mil-spec FKM family, including M83248 and AMS7276, covers standard FKM only. ETP is bought to a customer drawing or by trade designation instead. See the mil-spec reference for what those specs actually cover.

If your drawing calls out a specific spec or compound, tell us and we will match it, with a Certificate of Conformance and lot traceability under our ISO 9001:2015 system.

Typical applications by industry

See O-Rings by Industry for the wider picture, or browse all materials to compare.

Is Viton® ETP the right choice?

Three questions settle it:

1. Does your fluid include bases, amines, ketones, esters, or alcohols? If not, standard FKM almost certainly covers you for less money. Buy that.
2. Does it also include acids, fuels, or hydrocarbons? If yes, ETP’s combination is hard to match, and this is where it beats swapping to EPDM.
3. Is the service cold? If the seal sees anything much below freezing, ETP is the wrong material regardless of how good the chemistry story looks.

If the answers point to ETP, the last check is price against FFKM. ETP is the bridge: broader than FKM, cheaper than FFKM, and for a great many jobs it is enough. When it is not, we will tell you to spend the money on FFKM instead.

Not sure whether ETP covers your chemistry, or whether standard Viton® would do? Send us the conditions: the media, the temperature, the pressure, and whether the seal moves. We will spec the compound and the size with you, and we will tell you when the cheaper material is the right one. We make getting O-Rings easy.

General FKM polymer chemistry, fluorine content, the destructive effect of amines on standard FKM, and its strong swell in ketones and esters: Freudenberg FST 2025 Technical Manual, ch. 2 (Materials and Process Engineering), §3.4, p. 66. ETP-specific properties, grades, and ranges reflect Chemours product literature and the wider specialty fluoroelastomer market. The datasheet for your specific compound always governs; test parts in your actual service conditions before committing to a critical seal.