Fluorosilicone

What is Fluorosilicone?

Fluorosilicone is a specialised elastomer that combines the wide temperature resilience of silicones with the superior fuel, oil, and solvent resistance typically associated with fluorocarbon rubbers. In technical terms, it is classified under ASTM D1418 as FVMQ.

Fluorosilicone O‑rings, gaskets, and mouldings are usually blue (or light blue) by standard convention.

Because of this unique hybrid performance profile, Fluorosilicone is often the elastomer of choice for demanding static sealing applications — especially where exposure to fuels, oils, solvents or extreme temperatures is expected.

Key Properties & Performance Profile

Fluorosilicone delivers a range of performance attributes that make it valuable in many applications — but it also has limitations that designers should carefully consider.

Strengths & Advantages

• Broad Temperature Range: Fluorosilicone remains functional across a wide temperature span. Typical continuous-service ranges are around –55 °C to +205 °C (some compounds even wider), making it suitable for both low‑ and high‑temperature environments.
• Excellent Fuel, Oil & Solvent Resistance: It shows strong resistance to automotive and aviation fuels, oils (both mineral and synthetic), solvents, and non‑polar chemical media — making it ideal for fuel systems, hydraulic systems, and chemical exposure scenarios.
• Good Weathering, Ozone & UV Resistance: Fluorosilicone is resistant to ozone, sunlight, and weathering, which helps maintain integrity over time in outdoor or exposed environments.
• Stable Mechanical & Elastic Properties Over Temperature: Its mechanical properties (e.g. elongation, resilience) remain relatively stable even across temperature extremes — useful in applications like diaphragms or static seals that may see thermal cycling.
• Good Dielectric / Electrical Insulation Properties: Like silicone, Fluorosilicone remains a good electrical insulator, which can be beneficial in applications where electrical isolation is required.
• Suitability for Static Seals: Given its strengths, Fluorosilicone is often used for static sealing applications — e.g. O‑rings, gaskets, seals in fuel and fluid systems.

Typical Grades, Standards & Hardnesses

Fluorosilicone is available in a variety of hardness grades — provided as O‑rings, gaskets or custom mouldings — to suit different sealing demands.

Range of other commonly referenced physicals (depending on compound) — typical for many FVMQ rubbers — include tensile strength up to ~9 MPa, elongation at break around 200–400%, and elongation/ resilience properties comparable to silicone rubbers.

Common Applications & Typical Use Cases

Because of its unique blend of thermal resilience, chemical resistance and elasticity, Fluorosilicone finds use in a variety of demanding environments:

• Aerospace & Aviation: Seals, gaskets and O‑rings in aircraft fuel systems, hydraulic systems, and di‑ester lubrication applications — often subject to fuel, solvent, oil exposure and wide temperature swings.
• Automotive & Fuel Systems: Fuel‑system seals, gaskets, diaphragms, and static sealing components in engines or fuel delivery systems.
• Industrial & Chemical Processing: Seals in tanks, pipes or systems where exposure to mineral oils, non‑polar solvents, petroleum-based fluids or mild chemical media is expected.
• Outdoor / Environmental Applications: Due to its ozone, UV, and weathering resistance, Fluorosilicone is suitable for seals or gaskets used outdoors or in harsh environmental conditions.
• Static Sealing Systems (O‑rings, Gaskets, Diaphragms, Sheets): In many cases, Fluorosilicone is used for static seals rather than dynamic applications — whether in fuel tanks, flanges, housings, or static interfaces.

Given its limitations (e.g. poor abrasion/tear resistance), Fluorosilicone is not generally recommended for high‑wear or dynamic sealing applications, such as rotary shafts, reciprocating pistons, or where seal movement is frequent/continuous.

Design & Selection Considerations

When specifying Fluorosilicone seals for a given application, it’s important to:

• Consider the chemical environment carefully — while Fluorosilicone offers broad resistance to oils, fuels, non-polar solvents and many hydrocarbons, it may perform poorly when exposed to brake fluids, ketones, certain organic acids/aldehydes, or aggressive oxidising chemicals.
• Use it for static sealing wherever possible — due to limited abrasion and tear resistance, static seals (O‑rings, gaskets, flanges) are ideal. Avoid dynamic sealing (rotary shafts, pistons) unless operating conditions are mild and seal movement is minimal.
• Select the right hardness (Shore A) for the job — harder compounds may offer increased durability or sealing force, but softer compounds may seal better against irregular surfaces or under low‑temperature conditions.
• Acknowledge the limits of mechanical strength and gas permeability — if high mechanical loads or gas-tightness (e.g. vacuum or high-pressure gases) are required, other elastomer types (or composite/encapsulated seals) may be more appropriate.
• Verify with actual material data sheets from your supplier — as with any elastomer, final properties can vary depending on compound formulation, fillers, curing method, and supplier source.

Summary — Why Choose Fluorosilicone?

Fluorosilicone represents a versatile, high‑performance elastomer that delivers the best of both worlds: the thermal flexibility and dielectric properties of silicone, combined with the oil, fuel and solvent resistance typically associated with fluorocarbons.

For static sealing applications across aerospace, automotive, industrial and chemical sectors — especially where exposure to fuel, oil, solvents or wide temperature variation is expected — Fluorosilicone is often the material of choice.

However, designers must take care: it is not a universal solution. Its limitations in abrasion, tear strength, mechanical robustness and chemical compatibility with certain aggressive fluids mean that it should be deployed where its advantages matter most — and avoided in high‑wear, high‑stress, or chemically aggressive dynamic environments.

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Due to limited physical strength, poor abrasion resistance, and high friction characteristics, these elastomers are not generally recommended for dynamic sealing. They are predominately designed for static sealing use. They are also not recommended for exposure to brake fluids, hydrazine, or ketones.

Please note: This Material Data Sheet section is to be used as a professional guide only. Eastern Seals (UK) Ltd may source their products from a variety of Quality Approved Suppliers and the data shown should not be relied upon by any purchaser without verification of material source.

ES REF	Colour	Temp Range	Hardness	Notes	Data Sheet
F60	BLUE		60	Fluorosilicone 60 shore for general use.	F60
F70	BLUE	-55°C to +205°C	70	Fluorosilicone 70 shore for general use.	F70
F80	BLUE	-60°C to +177°C	80	Fluorosilicone 80 shore for general use.	F80
F70 MIL-SPEC	BLUE	-60°C to +177°C	70	This compound meets MIL-DTL-25988C	F70 MIL-SPEC