Fluorosilicone (FVMQ)

The combination nothing else offers

Nitrile handles fuel and stiffens in serious cold. FKM handles fuel and heat and stiffens in serious cold too. Silicone stays flexible at -60 °C and dissolves in fuel. Fluorosilicone is the only common family that holds fuel resistance and cold flexibility at the same time, which is why aerospace specifies it and why almost nothing else does.

Where the application is static sealing in fuel at ambient or elevated temperature and cold flexibility is not a requirement, FKM will usually outperform it mechanically and cost less. The cold is the reason to pay for FVMQ.

How we compound and test it

FVMQ shares silicone's mechanical weakness and adds cost, so part design matters more than usual: section thickness, gland fill, and how the part is handled during assembly all affect whether it survives installation. We will flag a geometry that is going to tear during fitting before tooling rather than after.

For aerospace and defence programmes the documentation is as much of the deliverable as the part. Lot traceability, cure and post-cure records, and accredited test data come with it as standard, because those programmes buy the paperwork alongside the hardware.

The Lab

The two mistakes buyers make

The first is specifying it where FKM would do. If the part never sees serious cold, the fluorosilicone premium buys nothing and costs mechanical strength.

The second is assuming fluorinated means universally resistant. FVMQ is poor in brake fluids, ketones, and some phosphate esters. Fluorine on the label is not a blanket chemical warranty, and this is the family where that assumption bites most often.

Typical uses

• Aerospace fuel system seals and diaphragms
• Aircraft parts with cold-soak requirements
• Fuel-exposed parts needing low-temperature flexibility
• Defence programmes requiring documented specialty materials
• High-altitude and cryogenic-adjacent service