Which elastomer resists each fluid: a selection guide for silicone, FKM, FVMQ and EPDM

The problem nobody puts in the specification sheet

A typical specification sheet for a seal reads something like: 'material compatible with hydraulic oil, service temperature –20 °C to +120 °C, minimum service life 10 years'. What it does not state is which hydraulic oil exactly. And the difference matters: an HLP mineral oil to DIN 51524 is a relatively benign medium for a standard FKM, but a phosphate ester base hydraulic fluid (HFD-R) swells NBR, degrades neoprene and demands an FKM with fluorine content above 66 %. If the specification does not state it, selection error is guaranteed.

The same problem appears when the main fluid is not the only contact medium. A seal in a food process line may work with sunflower oil during production and then be exposed to 2 % NaOH during CIP cleaning, followed by rinsing with water at 85 °C. The material that resists vegetable oil is not necessarily the same that resists the full cycle. And when it fails — always during cleaning, never during production — the failure is attributed to a 'supplier quality issue' rather than to incorrect material selection.

This article provides the technical criteria to walk the path in reverse: from the actual service fluid — with all its variants, its temperature extremes and its cleaning cycles — to the specific elastomer that will solve the sealing problem without premature failure. There is no universal material. Each family has a domain of application and a defined limit where it stops working. Engineering means knowing both.

What really determines the chemical resistance of an elastomer

The chemical resistance of an elastomer is not a generic property: it depends on the interaction between the molecular structure of the base polymer, the nature of the fluid and the thermodynamic conditions of contact (temperature, pressure, concentration, time).

The main degradation mechanism is swelling by fluid absorption. When an elastomer contacts a liquid chemically compatible with its polymer chain, fluid molecules penetrate between the chains, increase the volume of the material, reduce the effective crosslink density and degrade mechanical properties. An elastomer that has absorbed 30 % of its volume in solvent no longer seals: it has lost recovery force, compression set and dimensional stability.

The practical rule governing this process is the like-dissolves-like principle: polar materials resist non-polar fluids and vice versa. A highly polar elastomer (such as NBR, which contains nitrile groups) resists non-polar mineral oils well, but swells in polar solvents like ketones. A non-polar elastomer (such as EPDM, based on ethylene-propylene chains) resists water and bases well, but non-polar hydrocarbons destroy it. FKM partially escapes this logic because the C–F bonds are exceptionally stable both energetically and sterically: fluorine atoms, bulkier than hydrogen, shield the main carbon backbone against chemical attack. Hence its resistance to an unusually wide spectrum of fluids.

The second relevant mechanism is direct chemical degradation: hydrolysis (breakdown by water, especially in the presence of acids or bases at temperature), oxidation (breakdown by oxygen or oxidising agents), and attack by amines or strong bases on cure systems. This mechanism does not manifest as swelling but as progressive loss of elasticity, surface cracking and, eventually, fragmentation of the material. Standardised swelling tests (ASTM D471) detect the first mechanism but not always the second, which makes validation under real service an unavoidable step for critical applications.

VMQ silicone: the thermal generalist that does not resist oils

Methyl vinyl silicone (VMQ) operates in a thermal range no other conventional elastomer matches: from –60 °C to +200 °C continuous with standard formulations (Series 1, 2, 4 and 12), down to –110 °C with phenylated PVMQ silicones (Series 5), and up to +300 °C continuous with high-temperature stabilised formulations (Series 9, with peaks at +315 °C). This thermal breadth makes it the first choice for any seal where temperature is the dominant variable and the medium is not chemically aggressive.

Silicone is also inherently resistant to ozone, UV radiation and weathering — it requires no antiozonants or stabilisers, unlike NBR and neoprene which need them to survive outdoors. It is inert against most dilute acids and bases, alcohols and water (including hot water and steam up to the temperatures specific to each formulation). Its compression set properties are predictable and stable over years of service, which makes it reliable in long-life static seals.

But VMQ silicone has a structural incompatibility with hydrocarbons. Mineral oils, fuels (petrol, diesel, kerosene), aliphatic and aromatic solvents and most mineral-base hydraulic fluids penetrate between the polysiloxane chains and cause swelling that can exceed 100 % of the original volume. The material completely loses its sealing capability. It is not a gradual degradation: at typical service temperatures (60–100 °C), a standard VMQ seal exposed to mineral oil can fail in days or weeks.

This incompatibility has no solution within the VMQ family. There is no hardness, formulation or additive that turns standard silicone into an oil-resistant material. When the fluid includes hydrocarbons, one must jump to another family: FKM if the minimum temperature is not an issue, or FVMQ fluorosilicone if low-temperature flexibility is also required.

FKM (Viton®): superior chemical resistance with a defined lower limit

FKM fluoroelastomer is the reference material for seals in chemically aggressive environments. Its fluorine content — typically between 64 % and 70 % depending on the polymer family — gives it chemical resistance that no other conventional elastomer matches across that range of media: aliphatic and aromatic hydrocarbons, fuels (petrol, diesel, kerosene, JP-8, biodiesel), mineral and synthetic oils, hydraulic fluids in virtually all families (HLP, HFC, HFD), dilute and concentrated mineral acids (H₂SO₄, HCl, HNO₃ in moderate concentrations), and chlorinated solvents.

The FKM thermal range spans –20 °C to +200 °C continuous service, with brief peaks up to +230 °C. The GLT and GFLT families extend low-temperature flexibility to approximately –40 °C, but with significantly higher cost and more limited availability. For most industrial applications, the practical lower limit of standard FKM (type A or type B) is –15 / –20 °C. Below that temperature, the material stiffens, loses elastic recovery and the seal stops working. It is not a catastrophic visible failure: there is simply leakage.

Where FKM does not work: ketones (acetone, MEK, cyclohexanone), esters (ethyl acetate, butyl acetate), aliphatic and aromatic amines, concentrated strong bases (NaOH >10 %, KOH >10 %), continuous water vapour above 150 °C in bisphenol-cured compounds, glycol-base brake fluids (DOT 3, DOT 4) and low-molecular-weight organic acids (concentrated acetic acid, formic acid).

These incompatibilities are neither minor nor theoretical. Acetone — a solvent present in a surprising number of industrial cleaning processes — produces swelling above 30 % in standard FKM in a matter of hours. And in an industrial context, contact with ketones often occurs not during normal service but during cleaning between batches, which makes the failure appear intermittent and hard to diagnose. Anyone needing more detail on the differences between generic FKM, European FPM and the various Viton™ grades can consult our technical article on FKM, FPM and Viton™, which breaks down the nomenclature, the cure systems and the criteria for deciding when to specify a brand and when an ASTM specification suffices.

For compressible seals where FKM needs to adapt to surface irregularities or seal under low closing force, the alternative is sponge Viton® sheet: closed-cell structure with integral skin combining the compressibility of a cellular material with the chemical resistance of the fluoroelastomer.

FVMQ fluorosilicone: the material that fills the gap between VMQ and FKM

Fluorosilicone (FVMQ) exists because there is a functional space that neither VMQ silicone nor FKM covers: seals that simultaneously require hydrocarbon resistance and low-temperature flexibility.

FVMQ incorporates trifluoropropyl groups (–CH₂CH₂CF₃) in the polysiloxane chain. This modification gives the material resistance to mineral oils, fuels, aliphatic solvents and most hydraulic fluids — media that destroy standard VMQ silicone. But by retaining the silicone base structure, it keeps the low-temperature flexibility that FKM cannot offer: FVMQ works from –60 °C to +170 °C, extendable to +220 °C with high-temperature additives (Series 13 in the Progress Silicones catalogue).

The clearest use case is aerospace. A seal in the hydraulic system of a landing gear operates with Skydrol fluid (phosphate ester) or MIL-PRF-5606 (mineral oil) at temperatures that in flight at cruise altitude can drop to –50 °C and during braking operations can exceed +100 °C. Standard FKM, rigid at –20 °C, does not work. VMQ silicone, which swells in hydraulic fluid, does not work either. Fluorosilicone solves the problem. The same reasoning applies in engine compartments of industrial vehicles operating in cold climates, rail hydraulic systems outdoors, and any application where exposure to oils or fuels coexists with low-temperature cycles.

The main limitation of FVMQ is mechanical. Its tear strength is below that of FKM and standard VMQ silicone: typically 8–15 kN/m versus 20–35 kN/m for FKM or 20–30 kN/m for the best VMQ formulations (Series 12). This rules it out for seals subjected to dynamic tensile loading or severe abrasion. It also has lower resistance to ketones, amines and chlorinated solvents — in those media, fluorosilicone fails as FKM does.

FVMQ is available in our catalogue as Series 13 formulation, processable by extrusion (tubing, profiles, cords) and moulding.

EPDM: water, steam and ozone — and nothing else

Ethylene-propylene-diene (EPDM) dominates a very defined territory: anything involving water, steam, bases, dilute acids, ozone and weathering, provided no hydrocarbons are present.

The structure of EPDM — a saturated ethylene-propylene chain with crosslinking points on the diene — gives it exceptional resistance to oxidation, ozone and UV radiation. Unlike NBR and neoprene, EPDM does not need antiozonants to survive outdoors: the saturated chain does not present the double bonds that ozone attacks. This makes it the material of choice for construction seals, HVAC, automotive (oil-free cooling circuits), plumbing and water treatment.

In hot water and steam, EPDM works up to 150 °C continuous with standard peroxide-cured formulations. Special grades designed for prolonged steam reach 180 °C. It resists well the alkaline detergents and cleaning products typical of CIP processes in food and pharmaceutical industries, as well as the dilute acids used in rinsing and disinfection.

But EPDM is structurally incompatible with hydrocarbons. Mineral oils, fuels, aliphatic and aromatic solvents swell and degrade it rapidly and irreversibly. An EPDM seal exposed to traces of mineral oil in a water circuit does not last months — it lasts weeks. And the failure is not always evident: the material swells, loses compression force, and the leak appears progressively without visible rupture. This is especially insidious in industrial water circuits where oil contamination may be intermittent and undocumented.

Available as EPDM sheet for cut flat gaskets, and as extruded profiles and moulded parts in various hardnesses and formulations.

NBR: oil resistance at optimised cost with environmental limits

Nitrile rubber (NBR) owes its oil resistance to the nitrile groups (–C≡N) in its acrylonitrile chain. The higher the acrylonitrile (ACN) content, the higher the resistance to oils and fuels, but the lower the low-temperature flexibility. Standard grades range from 28 % to 45 % ACN: an NBR with 34 % ACN offers a good general compromise; a 45 % ACN grade resists aromatic fuels better but stiffens at moderately negative temperatures.

The thermal range of standard NBR spans –30 °C to +100 °C. Special grades reach +120 °C, but above that temperature the material ages in an accelerated manner: crosslinking progresses, the material hardens and cracks. It is not a safety limit — it is a service-life limit. NBR at 130 °C may work initially and fail after 3–6 months due to thermal ageing.

The advantage of NBR over FKM is cost: a good-quality NBR compound costs between 60 % and 80 % less than an FKM. For industrial applications where the temperature does not exceed 100 °C, the medium is mineral oil, grease or aliphatic fuel, and the seal is protected from direct exposure to ozone and UV, NBR is the economically rational choice. Specifying FKM where NBR meets the technical requirement is overdesigning without functional benefit.

The critical limitation of NBR is its vulnerability to ozone and weathering. The residual double bonds of butadiene in the polymer chain are attack points for ozone: outdoors or near electrical equipment that generates ozone (motors, frequency drives), NBR develops surface ozone cracking within months. Antiozonants help but do not eliminate the problem. For outdoor use, EPDM or neoprene are preferable.

Neoprene CR: the compromise that works until it does not

Polychloroprene (CR, Neoprene®) is the general-purpose elastomer par excellence. It is not the best in any individual category, but it offers moderate simultaneous resistance to oils, ozone, weathering, flame and abrasion. This versatility makes it the most specified material when the specification does not precisely define the contact medium or when the application involves moderate exposure to multiple agents.

The thermal range of CR spans –35 °C to +120 °C. It resists mineral oils moderately (swelling of 10–25 % depending on oil and temperature, versus

The limit of neoprene appears when conditions become specific. If the oil is aromatic, CR fails. If the temperature rises to 130 °C, CR ages rapidly. If food or medical certification is required, CR does not have the necessary approvals. If the requirement is fuel resistance in immersion, FKM is clearly superior. Neoprene works in the grey zone where no other material can be justified by cost or specification: general machinery, construction, mining, conveyor belts, coatings, generic industrial seals.

Viton™ A versus Viton™ B: what changes between FKM families

Within the Viton™ range from Chemours — the most widespread FKM brand — the two families most widely used industrially are type A and type B. The difference is concrete and has direct implications for performance:

Viton™ type A is a VDF/HFP copolymer (vinylidene fluoride and hexafluoropropylene) with a fluorine content of 66 %. It is the general-purpose grade. Good resistance to most oils, aliphatic fuels and hydraulic fluids. It is the reference material when the specification says 'FKM' without further detail. Moderate cost within the FKM family.

Viton™ type B is a VDF/HFP/TFE terpolymer (adds tetrafluoroethylene) with a fluorine content of 68 %. The higher fluorine content and the incorporation of TFE improve resistance to aromatic hydrocarbons, chlorinated solvents and concentrated acids. Type B is the grade specified when the medium includes toluene, xylene, dichloromethane or fuel blends with high aromatic content. It is also the preferred grade for aerospace applications (AMS 7276) where material traceability is a documentary requirement.

The practical difference: if a type A seal exposed to a fuel blend with 30 % aromatics shows a swelling of 15 % after 168 h at 23 °C (ASTM D471), the same test with type B can give a swelling of 8–10 %. In applications where dimensional tolerance is critical — injector seals, fuel valve gaskets, aerospace hydraulic system seals — that 5–7 percentage-point difference makes the difference between a seal that works 15 years and one that needs replacing at 5.

At ProSilicones64 we work with Viton™ B as the standard for our FKM flat gaskets, precisely because the cost premium of type B over type A is moderate (15–20 %) and the gain in chemical resistance justifies it in virtually all applications that reach our technical department. When the application does not require type B performance, we offer generic FKM to ASTM specification — no brand cost but with the guarantee of a 100 % virgin FKM compound.

Decision tree: from fluid to material in four steps

The selection sequence does not start with the supplier's catalogue — it starts with the fluid.

Step 1. Identify the dominant fluid. The most aggressive medium to which the seal will be exposed determines the material family. If there is more than one medium (service + cleaning, for example), the most aggressive prevails. A seal that works with water during production and is exposed to 2 % NaOH during CIP must resist both. A seal that works with oil during service and is cleaned with acetone has a problem that cannot be solved with a single elastomer.

Step 2. Determine the actual thermal extremes. Not the 'nominal' process temperature, but the actual minimum (cold start-up, winter storage, overnight shutdown) and the actual maximum (process peaks, cleaning, sterilisation). An installation in Zaragoza with cold starts at –8 °C in January is outside the range of standard FKM if the seal needs to function during start-up. An installation in Bilbao that washes with steam at 134 °C every shift requires a material that withstands those cycles, not only the 80 °C process temperature.

Step 3. Discard incompatible materials. A single incompatible medium eliminates the candidate. There is no useful 'partial resistance' in a seal: either the material is compatible with the fluid throughout the life of the seal, or it is not.

Step 4. Select among the survivors by cost, availability of certified formulations (FDA, EN 45545-2, USP VI, ISO 10993), secondary mechanical properties (tear, compression set, required hardness) and available manufacturing format (extrusion, moulding, sheet cutting).

The most frequent paths

• Hydrocarbons, oils, fuels with T min > –20 °C → FKM. If the application requires OEM traceability or superior resistance to aromatics, Viton™ B. If cost is decisive and the specification is open, generic FKM to ASTM D1418.
• Hydrocarbons, oils, fuels with T min < –20 °C → FVMQ fluorosilicone. If FVMQ mechanical properties are insufficient, evaluate FKM GLT/GFLT grades (down to –40 °C, premium cost and limited availability).
• Hot water, steam, bases → EPDM up to 150–180 °C. If an extended thermal range is also required below –40 °C or above +200 °C, VMQ silicone with the appropriate formulation.
• Oils at moderate temperature (
• Mixed environment with moderate aggression, critical cost → Neoprene CR as a compromise. Validate case by case that the moderate resistance of CR is sufficient for the actual media.
• Ketones, amines, concentrated strong bases → No conventional elastomer simultaneously solves ketones + temperature + elastic sealing. For pure ketones, evaluate encapsulated PTFE, FFKM (perfluoroelastomer, cost 10–30 times that of FKM, outside our catalogue) or system redesign to avoid contact between the seal and the medium.

What no compatibility table replaces

Chemical resistance tables — including those in this article and those from compound manufacturers — work with immersion data in pure fluids at standardised temperatures over standardised times (typically 168 h or 672 h to ASTM D471). Actual service conditions rarely match the test conditions.

Three variables tables do not capture

Fluid mixtures. A mixture of two individually compatible fluids can produce negative synergies not predicted by individual tests. The additives in industrial oils (antioxidants, detergents, viscosity index improvers) modify the aggressiveness of the medium relative to the pure base oil.

Thermal and concentration cycles. A seal that works at 80 °C during production and is exposed to steam at 134 °C for 30 minutes every 8 hours ages differently from one that works continuously at 134 °C. Cyclic thermal stress can be more aggressive than a higher continuous temperature.

Simultaneous mechanical loading. An elastomer under 25 % compression set that is also exposed to an aggressive fluid degrades faster than the same material in a free immersion test. Compression opens diffusion paths that accelerate fluid absorption. Swelling data on free specimens underestimates the actual effect on an installed seal.

For applications where seal failure has consequences — safety, regulation, downtime cost, product contamination —, validation under actual service conditions before specifying the definitive material is not a recommendation: it is an engineering requirement.