Fluorosilicone (FVMQ)
Fluoro Vinyl Methyl Silicone | FLS | ASTM D1418: FVMQ
Fluorosilicone is a specialty elastomer built for a specific and narrow application domain: sealing where both extreme temperature range and fuel or oil resistance are simultaneously required. Standard silicone (VMQ) handles the temperature range but not the fuel; standard FKM handles the fuel but not the extreme low-temperature end. FVMQ is the solution when both conditions are present in the same application.
Wayne Rubber manufactures custom FVMQ o-rings, gaskets, seals, and diaphragms in Wixom, Michigan. FVMQ’s polymer structure, limitations, and the specific application profile where it is genuinely superior to both VMQ and FKM are all covered below. This is a material that should be specified when the application genuinely requires it, not as a general upgrade from standard silicone.
What FVMQ Is and Why It Exists
Standard silicone rubber (VMQ) is built on a silicon-oxygen (Si-O) backbone with methyl and vinyl side groups. The Si-O backbone provides VMQ’s extraordinary temperature range and chemical inertness; the nonpolar methyl side groups give it no resistance to petroleum-based fuels and oils, which dissolve into the polymer and cause significant swell.
Fluorosilicone is produced by replacing some of the methyl side groups with trifluoropropyl groups. The trifluoropropyl group contains three fluorine atoms, which are highly electronegative and polar. These fluorine-bearing side groups repel nonpolar hydrocarbon molecules (fuels, oils) much as the ACN groups in nitrile rubber do; they are chemically incompatible with non-polar hydrocarbons and resist their penetration into the polymer. The Si-O backbone remains intact and unchanged, preserving VMQ’s temperature range, low-temperature flexibility, ozone resistance, and UV stability.
The consequence is a polymer that simultaneously offers silicone’s temperature range and fuel resistance at a level approaching nitrile rubber, but the fluorine addition is not free. The bulky trifluoropropyl groups stiffen the polymer chain slightly, which reduces the upper temperature limit relative to standard silicone from approximately 500°F to approximately 400°F continuous. They also reduce thermal stability in pure hot-air aging; FVMQ does not age as well in sustained dry heat as standard VMQ. This is a counter-intuitive but important limitation: FVMQ is slightly inferior to VMQ in hot-air oven aging despite its higher overall performance envelope.
The fluorine groups also increase the compound’s density and cost. FVMQ compounds cost significantly more than equivalent VMQ compounds, typically two to four times more. The premium is justified when the application genuinely requires both fuel resistance and silicone’s extreme low-temperature flexibility. For applications where only one of those properties is needed, VMQ or FKM is more cost-effective.
VMQ vs. FVMQ vs. FKM: The Three-Way Decision
FVMQ exists specifically to address the application space where both VMQ and FKM individually fall short. Understanding where each of the three materials excels and where each fails is the starting point for any specification decision involving these compounds.
FVMQ Chemical Resistance Summary
| Fluid / Environment | Resistance | Notes |
|---|---|---|
| Aviation Fuels (Jet A, JP-4, JP-5, JP-8) | Excellent | FVMQ is the standard elastomer for aviation fuel system seals. Aviation fuels have high aromatic content that would cause unacceptable swell in standard silicone. FVMQ provides the fuel resistance of a fluorocarbon compound while retaining silicone’s extreme temperature range, the two properties simultaneously required for airframe and engine fuel system sealing. Meets AMS 3325/3326/3327 and MIL-DTL-25988 specifications for aviation fluorosilicone applications. |
| Petroleum Fuels (gasoline, diesel) | Good | Good resistance to automotive gasoline and diesel fuels. Used in automotive fuel injector o-rings and fuel system seals in applications where operating temperature exceeds FKM’s low-temperature limit or where the wide temperature cycling range of a vehicle in cold climates makes FKM’s stiffness at cold-start a sealing concern. Modern biofuel blends (E10, E15, B20) perform well with FVMQ. |
| Mineral Oils and Hydraulic Fluids | Good | Good resistance to mineral oils and petroleum-based hydraulic fluids. Suitable for hydraulic system seals in aircraft and high-altitude equipment where both fuel contact and extreme low-temperature service are present. Not as oil-resistant as high-ACN FKM in concentrated mineral oil immersion; for pure hydraulic oil service without extreme low-temperature requirements, FKM is preferred. |
| Di-Ester Lubricants (MIL-PRF-23699) | Excellent | Outstanding resistance to di-ester synthetic lubricants such as MIL-PRF-23699 aircraft engine oils that cause significant swell in standard silicone. This resistance, combined with the temperature range, makes FVMQ the standard for aircraft engine oil system sealing adjacent to components that also see fuel exposure. |
| Ozone, UV, Weather | Excellent | FVMQ inherits VMQ’s outstanding ozone and UV resistance. The Si-O backbone contains no double bonds susceptible to ozone attack. Long outdoor service life without surface cracking. |
| Hot Air (sustained, above 350°F) | Fair (below VMQ) | This is FVMQ’s most counter-intuitive limitation. In sustained dry hot-air aging, FVMQ performs slightly worse than standard VMQ because the trifluoropropyl groups are less thermally stable than methyl groups in pure oxidative conditions. For applications with continuous dry heat above approximately 350°F without fuel contact, standard VMQ is a better choice than FVMQ. FVMQ’s 400°F upper limit should be treated as the practical maximum for sustained dry service, not the continuous service design point. |
| Ketones and Esters | Poor | Ketones and esters cause significant swell in FVMQ, the same limitation shared with standard FKM. FVMQ is not suitable for applications involving ketone-based cleaning solvents or process fluids. If ketone resistance is required alongside extreme temperature range, FFKM is the only option. |
| Phosphate Ester Hydraulic Fluids (Skydrol) | Poor | Like standard FKM, FVMQ has poor resistance to phosphate ester hydraulic fluids. EPDM is the correct specification for Skydrol and phosphate ester fluid service. This is an important point in aviation maintenance; FVMQ must not be substituted for EPDM in phosphate ester hydraulic systems despite being used elsewhere in the same aircraft. |
| Aqueous Solutions, Dilute Acids/Alkalis | Moderate | Moderate resistance to dilute aqueous chemistry at ambient temperatures, similar to standard VMQ. Not suitable for concentrated acid or strong alkali service. |
| Abrasion Resistance | Poor | Like standard VMQ, FVMQ has poor abrasion resistance. It is primarily suited to static sealing applications. Dynamic applications with surface sliding contact or abrasive exposure are not appropriate for FVMQ without carefully evaluating the specific contact conditions. For dynamic seal applications, FKM provides better mechanical durability. |
FVMQ Capabilities and Limitations
- Temperature Range: -85°F to +400°F continuous; the widest range of any fuel-resistant elastomer
- Fuel Resistance: aviation fuels (Jet A, JP-4/5/8), gasoline, diesel, and di-ester synthetic lubricants
- Low-Temperature Advantage: remains flexible at -85°F, covering arctic cold-soak conditions that cause FKM to harden
- Static Sealing Only: poor abrasion resistance limits FVMQ to static or very low-motion sealing applications
- High Gas Permeability: not suitable for high-pressure gas or vacuum sealing requiring low permeability through the seal body
- Hot-Air Aging: slightly inferior to VMQ in sustained dry heat above 350°F without fuel contact
- Ketone Incompatibility: ketones, esters, and phosphate ester hydraulic fluids cause degradation
- Low Tensile/Tear Strength: similar to standard VMQ; significantly lower than FKM
- High Shrinkage: FVMQ compounds have higher mold shrinkage than VMQ or FKM; tooling must account for material-specific shrinkage values to achieve dimensional targets
- Cost: significantly higher than VMQ; should only be specified when the dual temperature-and-fuel requirement genuinely cannot be met by VMQ or FKM alone
- Aerospace Specifications: available to AMS 3325/3326/3327 and MIL-DTL-25988 for military and aerospace qualification requirements
- Cure Systems: peroxide or platinum addition cure, same as standard VMQ; addition cure preferred for low-extractable applications
Fluorosilicone (FVMQ) Applications
Fluorosilicone Products from Wayne Rubber
Wayne Rubber manufactures custom FVMQ components for static sealing applications in aviation, aerospace, and automotive fuel systems. Provide the fuel type, temperature range, aerospace specification (AMS or MIL), and dimensional drawing when requesting a quote.
Request Custom FVMQ Parts from Wayne Rubber
Provide your part drawing, fuel type, temperature range (particularly the minimum cold-soak temperature), and any aerospace specification (AMS or MIL). Wayne Rubber will confirm FVMQ is the correct compound and quote.