Reference guide
O-Ring Chemical Compatibility Guide
Match the O-ring material family to the media first: nitrile and FKM (Viton®) resist petroleum oils and mineral hydraulic fluid, FKM also resists gasoline and diesel, EPDM handles water, steam and glycol brake fluid but never petroleum oil, and FFKM rates well against nearly every media family at a much higher cost. The ratings on this page are general guidance for each family at moderate temperature; temperature, concentration and whether the seal moves change them, and the compound datasheet confirms the choice.
Chemical compatibility is the first question in O-ring material selection and the one most often answered from memory. This guide gives a first-pass screen for the five common O-ring materials against the everyday media families, explains how to read a compatibility rating and what changes it (temperature, concentration, static or dynamic service), and lists eight compatibility traps covered in the Parker® O-Ring Handbook (ORD 5700). Ratings here are general guidance for the material family at moderate temperature; specific compounds, concentrations and temperatures change the answer, so confirm against the compound datasheet before finalizing a seal.
First-pass screen by media family
Use this table to narrow the material choice, never to finalize it.
A = excellent · B = good · C = conditional, verify grade · X = not recommended
| Media | Buna-N | Viton | EPDM | Silicone | FFKM |
|---|---|---|---|---|---|
| Petroleum oils and greases | A | A | X | C | A |
| Gasoline and diesel fuels | C | A | X | X | A |
| Hydraulic fluid (mineral oil) | A | A | X | C | A |
| Water (to about 82 C / 180 F) | A | C | A | A | A |
| Steam | X | X | A | C | B |
| Glycol brake fluids | X | X | A | C | C |
| Dilute acids | C | C | A | B | A |
| Ketones (acetone, MEK) | X | X | B | X | A |
| Alcohols | B | B | A | B | A |
| Ozone and weathering | X | A | A | A | A |
Material detail pages: Buna-N, Viton, EPDM, silicone, FFKM.
How do you read a compatibility rating?
A rating summarizes how much an elastomer swells, softens, hardens or loses strength after immersion in a medium, usually at one temperature and one concentration, measured by a fluid-immersion test such as ASTM D471. The letters mean different things in different manufacturers' charts, so read the legend, and read the conditions. A compound's ASTM D2000 line callout encodes the same idea in shorthand: the class letter states the maximum volume swell in reference oil, and the EA, EF and EO suffixes name the aqueous, fuel and oil immersion tests the compound passed. The Parker O-Ring Handbook sets out how much change a seal can tolerate.
| Factor | Rule of thumb | Source |
|---|---|---|
| Swell in static service | Roughly 25 to 30 percent volume swell is tolerable in a static seal | Parker ORD 5700 section 10 failure table |
| Swell in dynamic service | Roughly 10 percent; a swollen ring drags, extrudes and abrades | Parker ORD 5700 section 10 |
| Shrinkage and hardening | A medium that extracts plasticizer leaves a hard, shrunken, cracked ring; as bad as swell | Parker ORD 5700 section 10 |
| Temperature | Ratings are for room temperature and can fall at service temperature; test at the service temperature | Parker ORD 5700, section 3.14 (page 3-21) and Figures 3-12 and 3-13 |
| Concentration | Dilute and concentrated acid are different media; the handbook routes dilute hot acid to EPDM and concentrated room-temperature acid to acid-grade FKM | Parker O-Ring Handbook (ORD 5700) |
| Mixtures | A system that sees oil and water, or oil and steam, is judged on the worst component | Parker ORD 5700 section 2 |
| Compound, not family | Ratings are for the polymer family; a specialty compound (steam FKM, acid FKM, peroxide EPDM) can move a grade | Compound datasheets |
The eight compatibility traps
Eight common mistakes, each covered in the Parker O-Ring Handbook (ORD 5700).
| Trap | What happens | What the Parker handbook points to |
|---|---|---|
| EPDM in petroleum oil | Swells and fails; the number one failure | Nitrile or FKM |
| Plain nitrile outdoors | Cracks in ozone and sunlight | EPDM (no oil), HNBR or FKM (oil) |
| "Viton handles everything" | Hot water, steam, acetone, MEK, amines and brake fluid all defeat FKM | EPDM for steam and brake fluid; EPDM or FFKM for ketones; FFKM for amines |
| Silicone in a moving seal or in fuel | Tears, abrades, swells | Nitrile, FKM or fluorosilicone |
| Polyurethane in hot water | Hydrolyzes; the best abrasion material dissolves | Nitrile or HNBR |
| Nitrile or FKM in brake fluid | Attacked by glycol fluid | EPDM or butyl only |
| FFKM assumed universal | Fluorinated refrigerants (R11, R12, R13) are its one hole | Neoprene |
| Concentrated hot acid in any elastomer | Few elastomers survive; FFKM grades are rated for some | PTFE or metal seals |
Which material owns which media family?
The Parker handbook memory aid covers the three workhorses: nitrile resists oil but not weather, EPDM resists weather but not oil, FKM handles both but costs more. Extended to the other families:
| Media family | Handbook first option | Handbook second option | Avoid |
|---|---|---|---|
| Petroleum oils, greases, mineral hydraulic fluid | Nitrile (to 100 C) | FKM (to 204 C), HNBR (to 149 C) | EPDM |
| Fuels, especially aromatic and alcohol blends | FKM | Fluorosilicone (aerospace, low temperature) | EPDM, silicone |
| Water and hot water | EPDM | Nitrile (moderate temperature), silicone (static) | Polyurethane |
| Steam | EPDM steam grade (to 204 C) | FFKM steam grade where oil is also present | Nitrile, standard FKM, silicone |
| Glycol brake fluid, phosphate-ester hydraulic fluid | EPDM | Butyl | Nitrile, FKM |
| Ketones, esters, polar solvents | EPDM | FFKM | Nitrile, FKM, silicone |
| Aromatic and chlorinated solvents | FKM | FFKM | Nitrile, EPDM |
| Amines, mixed aggressive streams | FFKM | Aflas® (FEPM) per grade sheet | FKM |
| Dilute acids and alkalis | EPDM | FKM acid grade (concentrated, room temperature) | Polyurethane |
| Ozone, weather, sunlight | EPDM | FKM, silicone, HNBR | Plain nitrile |
| Refrigerants (ammonia, fluorinated) | Neoprene | HNBR (R134a) | FFKM with fluorinated refrigerants |
| Dry heat, no media | Silicone (static) | FKM | Nitrile above 100 C |
Temperature ceilings above are the Parker handbook standard ranges; the temperature range guide lists every material with its special-compound extents, and the comparisons (EPDM vs FKM, nitrile vs FKM, FFKM vs FKM, FKM vs silicone) walk the pairwise decisions.
These are published manufacturer guidelines, not Conquest Seal recommendations; Conquest quotes the material your print names.
What to send with a compatibility question
The medium by name and concentration (a trade name alone is not enough), the continuous and peak temperature, whether the seal is static or dynamic, the pressure, any secondary media (cleaning chemistry, flushing fluid, lubricant), and the AS568 size or the measured dimensions. With those, the compound your print names can be cross-referenced and quoted against its datasheet. Send them with a quote request.
Viton is a trademark of The Chemours Company; Aflas is a trademark of AGC Inc.; Parker is a trademark of Parker Hannifin Corporation. No affiliation or endorsement is implied.
Sources
- Parker O-Ring Handbook ORD 5700 (2021 printing), sections 2 and 10 (compound selection, compatibility and failure analysis)
- Parker O-Ring Handbook ORD 5700, section 2.2 (elastomer heat and cold figures), read 2026-09-14
- Parker compound E3609-70 datasheet (FDA), read 2026-08-13
- ASTM D2000 / SAE J200 line callout letters and suffixes; Parker O-Ring Handbook ORD 5700 (2021 printing), Table 8-5, pages 8-6 and 8-7 (ASTM D2000 callout format and suffix callouts); ASTM D2000-18(2024)e1 store listing
- ASTM D471 (fluid immersion test), named as the test method
Frequently asked questions
Is a compatibility chart enough to choose a material?
No. It narrows the family; the compound datasheet, the temperature and the duty finalize it.
Why do two manufacturers' charts disagree?
Different test temperatures, concentrations, immersion times and compounds. Read the conditions before comparing letters.
What is the safest material if I do not know the media?
There is none. FFKM comes closest chemically and still has a hole (fluorinated refrigerants); the only correct answer is to name the medium.
How much swell is acceptable?
Roughly 25 to 30 percent in a static seal and about 10 percent in a dynamic one, per the Parker handbook failure table; less is better in both.
Does temperature change compatibility?
Always, for the worse. Every rating in a chart applies at the temperature it was tested; heat accelerates swell and chemical attack.
Can a compliant food-grade compound still be incompatible?
Yes. FDA 21 CFR 177.2600 or NSF/ANSI 51 compliance says what may leach into food; it says nothing about what the seal survives. A compliant silicone still swells in oil. See the FDA and food-grade guide.
What is the D2000 oil-swell class, and how do I read it?
The class letter caps volume swell after 70 hours in the reference oil: B allows 140 percent, C 120, D 100, E 80, F 60, G 40 and K 10, while class A carries no oil requirement at all. So class A is the loosest cell on the chart, not the best, and an oil-service print should carry a letter well down the alphabet.
What does a typical 70 Shore A EPDM datasheet list as compatible?
Water-based service leads: hot water and steam, glycol brake fluids, alkaline cleaners and many acids. It also covers phosphate-ester hydraulic fluids, polar solvents such as alcohols, ketones and esters, and silicone oils and greases, with ozone and weather resistance. The one family it rules out is mineral oil products such as petroleum oils and greases (Parker compound E3609-70 datasheet, read 2026-08-13).
Which polymer families do the D2000 letter pairs map to?
The pairs are envelopes, not identities: BF, BG and BK cover nitrile, BA, CA and DA cover EPDM, BC and BE neoprene, FE and GE silicone, FK fluorosilicone, HK fluorocarbon and KK perfluoroelastomer, and BG covers polyurethane as well as nitrile. Matching the letters is a first screen; the compatibility of the actual compound is on its datasheet.
Related guides
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