You have an aerospace specification requiring VMQ silicone qualified to NF EN 2260, manufacture under EN 9100, batch-level traceability and a certificate of conformity per NF EN 9163. You open a generic industrial silicone catalogue and find none of this.
That is the problem. And it is the reason this guide exists.
Specifying an aerospace silicone is not a matter of selecting a catalogue material: it means simultaneously defining a qualified formulation, a cure system, a controlled manufacturing environment and a documentary chain that allows every part to be audited from compound mixing through to the assembly line. No generic silicone catalogue meets this level of requirement.
The difference between an industrial VMQ elastomer and an aerospace VMQ does not lie in the base polymer. It lies in the formulation qualified to NF EN 2259/2260/2261, the cure system (peroxide or platinum), the manufacturing environment in an ISO 8 cleanroom and the traceability dossier that accompanies every batch.
This technical guide is structured as a design office engineer would actually need it: first the regulatory framework to understand what is required, then selection by aircraft zone to identify which aerospace silicone is needed, and finally the verified technical data to enable precise specification.
- Why silicone dominates aerospace sealing
- Regulatory framework: certifications, qualifications and specifications
- Aerospace silicone selection by aircraft zone
- Peroxide vs. platinum cure: consequences in aerospace
- Comparative mechanical data for all series
- The aerospace traceability chain
- Common errors in aerospace elastomer specification
Why silicone dominates aerospace sealing
VMQ (Vinyl Methyl Silicone) has established itself as the reference elastomer for aerospace sealing owing to a combination of properties that no other polymer delivers simultaneously.
Thermal range: from −60 °C to +315 °C
The operational thermal range of an aerospace silicone extends from −60 °C to +300 °C in continuous service, with peaks up to +315 °C in specific high-temperature formulations. This range covers the entirety of an aircraft’s thermal zones: from the exterior fuselage at cruise altitude (where temperatures can fall below −55 °C) to areas adjacent to engines and bleed air ducts.
Ageing stability
Unlike conventional organic elastomers (NBR, EPDM, FKM), the Si–O–Si siloxane backbone of VMQ silicone confers intrinsic stability against degradation by ozone, ultraviolet radiation and thermal ageing.
On an aircraft with a service life of 25 to 30 years, this ageing resistance is a design factor, not a marketing argument.
Compression set and mass advantage
The low compression set of platinum-cured silicones enables the sealing function to be maintained over thousands of cabin pressurisation and depressurisation cycles.
The typical density of a solid silicone (1.10 to 1.20 g/cm³) also provides a mass advantage over fluorosilicones (1.40–1.46 g/cm³) and FKM fluoroelastomers (1.80+ g/cm³) in all applications where chemical resistance to fuel is not the determining factor.
Where standard VMQ silicone is not the answer
Not everything is solved with VMQ. Contact with aviation fuels, mineral oils or Skydrol-type hydraulic fluids degrades conventional silicone.
For these applications, specific alternatives exist within the same aerospace production environment: NBR elastomers qualified to NF L17-121 (Class 21, fuel resistance) and NF L17-123 (Class 23, hydraulic fluid resistance), or FVMQ fluorosilicones for zones combining partial hydrocarbon exposure with wide thermal range requirements.
Regulatory framework: what each standard means and where it applies
One of the most frequent errors in aerospace silicone specifications is confusing the three regulatory levels that apply to a component. A quality management system certification, a compound formulation qualification and a product delivery specification are not the same thing.
The standards table below distinguishes these three levels. Understanding this structure is the first step towards specifying correctly.
System certifications — how it is manufactured
System certifications apply to the production process, not to the material itself. A manufacturer may hold EN 9100 yet produce a silicone component that does not meet the client’s specifications if the formulation is not appropriate.
System certification guarantees that the process is controlled, auditable and repeatable — not that the material is correct for the application.
EN 9100 (scopes 50D and 61D). This is the reference quality management system standard for the aerospace sector, derived from ISO 9001 with additional sector-specific requirements. Scope 50D covers elastomer moulding and 61D covers extrusion.
A manufacturer may hold one or both, and the distinction matters: a moulded O-ring requires scope 50D; a continuous extruded profile requires 61D. Verifying that the supplier holds the correct scope for the type of part requested is the first filter in any aerospace silicone qualification process.
ISO 14644 (ISO 8 cleanroom). The ISO 8 classification per ISO 14644-1 limits the concentration of airborne particles in the manufacturing environment. For platinum-cured silicone components — where the catalyst is susceptible to inhibition by contaminants — cleanroom production is not a luxury but a process requirement.
NF EN 9103. Defines the method for controlling variation in key dimensional characteristics (Key Characteristics). For aerospace components where dimensional tolerances are critical to the sealing function, this standard establishes how variations are measured, controlled and reported.
Formulation qualifications — what the compound is made of
This regulatory level applies to the composition of the aerospace silicone compound. A formulation qualified to NF EN 2261 means that the specific silicone recipe (base polymer, fillers, vulcanising agent, additives) has been tested and validated against the requirements of that standard for VMQ elastomers at 70 IRHD.
NF EN 2259 / NF EN 2260 / NF EN 2261. These are the three standards in the series defining requirements for VMQ silicone elastomers intended for aerospace applications, differentiated by hardness:
- NF EN 2259: VMQ at 50 IRHD hardness (±5)
- NF EN 2260: VMQ at 60 IRHD hardness (±5)
- NF EN 2261: VMQ at 70 IRHD hardness (±5)
Each standard specifies the minimum requirements for mechanical properties (tensile strength, elongation at break, tear resistance), thermal ageing, compression set and resistance to specific fluids.
NF L17-106. This is the reference technical specification for NF L standardised aerospace rubbers, historically used in the Ariane programme specification documents.
NF L17-121 (Class 21) and NF L17-123 (Class 23). These apply to NBR elastomers — not silicones — and define requirements for applications requiring fuel resistance (Class 21) and hydraulic fluid resistance (Class 23). They are mentioned here because they frequently coexist with aerospace silicone components on the same aircraft.
Product and logistics specifications — how it is delivered
NF EN 9163. Defines the content and format of the aerospace certificate of conformity. This is the document that accompanies each delivered batch and contains the manufacturer’s declaration of conformity with the specified requirements.
NF L17-102. Establishes the marking and identification requirements for aerospace products: product reference, batch number, date of manufacture and expiry date.
NF L17-103. Defines the packaging and storage requirements for unmounted aerospace elastomers. Used particularly for Ariane programme components.
NF L17-104. Establishes the shelf life limit for aerospace rubbers. An aerospace elastomer that exceeds this date cannot be integrated into an assembly line.
Aerospace silicone selection by aircraft zone
Selecting the correct elastomer on an aircraft is not done by part type, but by service zone. An identical seal geometry may require completely different formulations depending on where it is installed.
Cabin and pressurised fuselage zone
Thermal range: −55 °C to +80 °C. Primary requirement: low compression set to maintain sealing integrity over thousands of pressurisation cycles. Recommended formulation: Series 12 (platinum VMQ, 20–90 Shore A). For door and window seals: Series 15 (platinum cellular VMQ).
Series 12 – Platinum silicone with good mechanical properties and versatility
High purity VMQ compound for extrusion and moulding, with high temperature option
View formulation →Engine and bleed air zone
Thermal range: +200 °C to +315 °C continuous. Primary requirement: prolonged thermal stability without mechanical degradation. Recommended formulation: Series 9 (peroxide VMQ, stabilised for high temperature). Post-cure mandatory to minimise volatiles.
Series 9 – Peroxide-cured silicone with excellent thermal resistance (300°C)
High-temperature VMQ compound for ovens, thermal gaskets, and moulded parts
View formulation →Fuel and hydraulic circuit zone
Standard VMQ silicone does not withstand aviation fuels or Skydrol-type hydraulic fluids. For these zones: NBR qualified to NF L17-121 (Class 21) for fuels, NBR per NF L17-123 (Class 23) for hydraulics, or FVMQ (Series 13) where a wide thermal range with partial hydrocarbon resistance is required.
Series 13 – Fluorosilicone (FVMQ) with high resistance to oils and solvents
Specific compound for chemically aggressive environments and hydrocarbon contact
View formulation →Avionics and connector zone
Primary requirement: EMI/RFI shielding. Recommended formulation: Series 11 (electrically conductive VMQ, volume resistivity ≤ 12 Ω·cm). Available exclusively in black owing to the conductive carbon filler.
Series 11 – Electro-conductive peroxide-cured silicone
Conductive VMQ compound with low resistivity for electrical applications
View formulation →Cryogenic zone and space applications
Thermal range: −110 °C to +215 °C. Primary requirement: flexibility at cryogenic temperatures. Recommended formulation: Series 5 (phenyl PVMQ). Applications: cryogenic propulsion circuit sealing, LOX/LH2 tank interfaces.
Series 5 – PVMQ (Phenyl) Silicone for extreme low temperatures (-110°C)
Specific compound for cryogenics and extreme cold applications maintaining mechanical properties
View formulation →Peroxide vs. platinum cure: consequences in aerospace
The cure system is not a manufacturing detail — it is a design decision that determines the maximum thermal range, outgassing level, cleanroom compatibility and available certifications.
Peroxide cure
Peroxide curing generates volatile by-products (organic acids) that require thermal post-cure for removal. In aerospace applications, this post-cure is mandatory: residual volatiles can contaminate optical surfaces, interfere with sensors or compromise coating adhesion.
The advantage: peroxide enables formulations stable up to +315 °C (Series 9) and is not susceptible to inhibition by contaminants. It is the reference cure system for engine and bleed air zones.
Platinum cure
Platinum curing (addition cure) does not generate significant volatile by-products. This makes it the preferred option for applications with purity requirements, low outgassing or contact with sensitive surfaces. Production must be carried out in an ISO 8 cleanroom.
Limitation: platinum catalysis is susceptible to inhibition by contaminants (sulphur compounds, amines, tin, PVC). The manufacturing environment must be strictly controlled.
Decision table: peroxide vs. platinum in aerospace silicone
| Criterion | Peroxide | Platinum |
|---|---|---|
| Maximum continuous temperature | +300 °C (Series 9) | +200 °C |
| Temperature peaks | +315 °C | Not recommended > +250 °C |
| Outgassing | Requires post-cure | Low, no post-cure required |
| Purity / Cleanroom | Compatible, with precautions | Native |
| Post-cure | Required | Not required |
| Sensitivity to contaminants | Low | High (platinum inhibition) |
| Space application (satellites) | Only with validated post-cure | Preferred |
| Engine / bleed air zones | Recommended | Not recommended |
Comparative mechanical data: all aerospace silicone series
The following table compiles the documented mechanical data for all silicone series relevant to aerospace and space applications, indicating the elastomer type, cure system and thermal range. All values correspond to manufacturer technical datasheet data, tested in accordance with the NF ISO standards indicated.
| Series | Type | Cure | Thermal range | Hardness (ShA) | Tensile (MPa) | Elongation (%) | Tear (kN/m) | Density (g/cm³) |
|---|---|---|---|---|---|---|---|---|
| Series 9 | VMQ | Peroxide | −60 to +315 °C | 40–68 | 6–8 | 300–400 | 12–17 | 1.11–1.20 |
| Series 12 | VMQ | Platinum | −60 to +200 °C | 20–90 | 6–9 | 100–1000 | 17–30 | 1.11–1.20 |
| Series 11 | Conductive VMQ | Peroxide | −50 to +210 °C | 50–70 | 5 | 100–250 | 5–10 | 1.11–1.16 |
| Series 15 | Cellular VMQ | Platinum | −60 to +200 °C | — | 3 | 600 | 15 | 0.50–0.80 |
| Series 5 | PVMQ | Peroxide | −110 to +215 °C | 50 | 8 | 550 | 28 | 1.21 |
| Series 13 | FVMQ | Peroxide | −60 to +220 °C | 40–70 | 6–7 | 160–400 | 10–21 | 1.40–1.46 |
| Series 10 | High tear VMQ | Platinum | −60 to +200 °C | 40–80 | 7–9 | 320–760 | 33–55 | 1.12–1.24 |
| Series 1 | High tear VMQ | Peroxide | −60 to +200 °C | 40–70 | 6–8 | 500–600 | 26–40 | 1.12–1.19 |
| Series 4 | Low CS VMQ | Peroxide | −60 to +200 °C | 40–80 | 6–7.5 | 100–350 | 10–15 | 1.11–1.40 |
Note: The values shown are documented minimums from the manufacturer’s technical datasheet. Final component properties depend on the processing conditions (moulding or extrusion), part geometry and first-article inspection testing per NF EN 9163. This document is not a certificate of conformity.
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View product →The traceability chain: from mixing to delivery
What distinguishes an aerospace silicone component from an industrial one is not only the material — it is the documentation that accompanies it. An aerospace quality engineer receiving a batch of silicone seals needs to be able to trace every part back to the compound formulation, the raw material batch, the manufacturing conditions and the dimensional inspection results.
The four documentary levels
Level 1 — Certificate of conformity (NF EN 9163). Issued exclusively following the manufacture and validation of the first production batch. It contains the declaration of batch conformity with the specified requirements, including the formulation reference, test results and batch identification.
Level 2 — Marking and identification (NF L17-102). Each part or batch carries permanent marking with traceability information: product reference, batch number, date of manufacture and storage expiry date.
Level 3 — Packaging and storage (NF L17-103). Components are packaged in accordance with programme requirements (Ariane specification for space components) with protection against light, ozone and mechanical deformation.
Level 4 — Shelf life control (NF L17-104). Aerospace elastomers have a shelf life limit that begins on the date of manufacture. Its management is a shared responsibility between the manufacturer and the integrator.
Common errors in aerospace elastomer specification
After years of working with design offices and procurement departments in the aerospace sector, certain aerospace silicone specification errors recur with sufficient frequency to warrant documenting them.
“60 Shore A silicone” without defining the cure system
A request stating “60 Shore A silicone seal” without indicating whether the application requires peroxide or platinum cure is akin to ordering “a bolt” without specifying the steel grade. The cure system determines the maximum thermal range, outgassing level, cleanroom compatibility and available certifications.
Machining tolerances on elastomer parts
Elastomers are not machined — they are moulded or extruded. The applicable tolerances are defined in ISO 3302: class M2 for moulded parts and class E1 for extruded parts. Specifying tolerances of ±0.01 mm on a silicone seal is not demanding, it is impossible.
Confusing formulation qualification with system certification
The fact that a manufacturer holds EN 9100 does not mean that all its formulations are qualified to NF EN 2259/2260/2261. System certification guarantees the process; formulation qualification guarantees the material. They are complementary, not equivalent.
Standard VMQ where FVMQ or NBR is needed
VMQ silicone does not resist aviation fuels or phosphate-ester hydraulic fluids. A VMQ silicone component installed in a fuel circuit will swell, lose mechanical properties and fail. Chemical compatibility is verified by testing in accordance with the applicable standard, not by assumption.
Ignoring shelf life
A stock of aerospace seals that has exceeded the NF L17-104 expiry date is lost stock. Shelf life management must be integrated into procurement planning from the specification phase, not discovered at the point of assembly.
Specifying by generic catalogue reference
Generic O-ring or profile catalogues offer “standard” silicone that is not qualified to aerospace standards. The fact that a catalogue silicone O-ring functions mechanically does not mean it is acceptable in an aerospace qualification dossier.
Verified production capabilities for aerospace silicone
The production infrastructure supporting these formulations includes active EN 9100 certification covering moulding (50D) and extrusion (61D) scopes, ISO 8 cleanroom production per ISO 14644, and an annual processing capacity exceeding 200 tonnes of elastomers with batch-level traceability.
Compound qualifications are validated in accordance with aerospace standards NF EN 2259, NF EN 2260 and NF EN 2261. Certificates of conformity are issued per NF EN 9163, exclusively following the manufacture and validation of the first production batch.
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