Thermoset Tubes for Aerospace — Materials, Qualification & Applications

Thermoset tubes in aerospace applications must combine low weight, high dielectric strength, dimensional precision, and resistance to the aggressive environments of aircraft service — MIL-I-24768-qualified G10, G11, and G7 grades are the backbone of aerospace wiring insulation, antenna feed-throughs, and structural electrical components.

TL;DR — Key Takeaways

• G10 (MIL-I-24768/14 GEE) and G11 (MIL-I-24768/15 GEB) tubes are the most common for aerospace electrical insulation; G11 is used when continuous temperature exceeds 130°C
• G7 (glass-silicone, MIL type GSG) is specified where service temperatures reach 180–220°C — engine bays, nacelle areas, proximity to heat-generating equipment
• Aerospace procurement requires Certified Test Reports (CTR), material traceability, and often QPL (Qualified Products List) sourcing
• Filament-wound tube construction is preferred for aerospace — controlled fiber angle provides optimized hoop-to-axial strength ratio for the specific loading
• Weight is a design driver — thermoset tubes offer better specific stiffness than aluminum at equivalent wall thickness for low-density axes

Why Thermoset Tube in Aerospace?

Weight and Specific Properties

Glass-epoxy (G10/G11) has a density of approximately 1.80–1.85 g/cc — lighter than aluminum (2.70 g/cc) and far lighter than steel (7.85 g/cc). For structural tubes that must also be electrically insulating:

Where insulation and structural function must be combined in one component, thermoset tube is often the only viable lightweight solution.

Electrical Isolation in Airframe Wiring

Lightning protection and HIRF (high-intensity radiated fields) management in aircraft require careful isolation of sensitive circuits from structure. Thermoset insulating tubes are used as:

• Conduit sleeves over wiring harnesses in areas where metallic conduit would create undesired ground paths
• Feed-through insulators where wiring passes through bulkheads
• Antenna support tubes — G10/G11 is transparent to RF at most aircraft frequencies

Grade Selection for Aerospace Applications

G10 vs G11 for Aerospace

The decision between G10 (GEE) and G11 (GEB) centers on continuous service temperature:

• G10 / GEE: Adequate for most avionics bays and cabin-zone electrical harness supports where ambient does not exceed 105–120°C
• G11 / GEB: Required for components near hydraulic lines, in hot sections of environmental control systems, or in regions adjacent to exhaust where ambient may reach 150–160°C

G11 uses a multifunctional epoxy with Tg of approximately 170°C versus G10's Tg of ~130°C. The mechanical and electrical properties are otherwise nearly identical.

G7 for Extreme Temperature Zones

G7 (glass-silicone) sustains 220°C continuous — the highest-rated standard thermoset tube. Used in:

• Engine bay harness insulators — around starter-generator wiring, oil-cooler connections
• Hot section bulkhead feed-throughs — engine compartment electrical penetrations
• Inertial platform insulation — IMU mounting fixtures that see thermal soaking

G7 is significantly more expensive than G10/G11 and should be reserved for the specific temperature zones that require it.

Qualification and Documentation Requirements

MIL-I-24768 Qualification

For DoD-funded aerospace programs, thermoset tubes typically must conform to MIL-I-24768. Requirements include:

1. Certified Test Reports (CTR): Mill test reports showing compliance with all required properties (dielectric strength, flexural strength, water absorption, flammability)
2. Material traceability: Lot number, laminator identity, date of manufacture traceable from part to CTR
3. QPL requirements: Some programs require the laminator to appear on the DLA Qualified Products List; verify QPL status with the applicable government contracting office

AS9100 / Nadcap Material Qualification

For AS9100-registered aerospace programs (commercial and military), the material qualification process includes:

1. First Article Inspection (FAI) of tube dimensions and properties
2. Review of laminator qualification and audit records
3. Lot-by-lot C of C and CTR review
4. Dimensional inspection per drawing — OD, wall thickness, ID, straightness, length

REACH and RoHS Compliance

Aerospace OEMs increasingly require material declarations for REACH SVHC substances. G10 and G11 (no brominated FR) are generally REACH-clean. FR4 (TBBPA-based) requires a declaration of TBBPA content — TBBPA is currently on the REACH candidate list for SVHC (candidate, not restricted as of 2026). Verify current status with your supplier for new program qualifications.

Dimensional Requirements for Aerospace Tube

Aerospace applications typically demand tighter dimensional tolerances than ASTM D709 standard:

Common Aerospace Thermoset Tube Applications

Wiring Harness Conduit and Sleeving

Used over wire bundles that pass through bulkheads or structure where metallic conduit would:

• Create bonding complications
• Cause RF shielding problems for antenna feedlines
• Add excessive weight in non-load-path runs

G10 or G11 tube, 1/2″–2″ OD, cut to length and passed through bulkhead penetrations with sealing grommets.

Antenna Radomes and Feed-Through Tubes

Tubes supporting antenna elements must be RF-transparent (low Dk, low tan δ). G10/G11 provides:

• Dk ≈ 4.5 (adequate for many antenna applications; lower-Dk materials available for high-frequency requirements)
• Low tan δ (0.012–0.020 at 1 MHz) — minimal signal attenuation

For frequencies above 3 GHz, lower-loss materials (PTFE-glass, ceramic-loaded composites) may be required, but G10/G11 covers most aircraft communication and navigation band applications (VHF/UHF/L-band).

Structural Electrical Insulating Spacers

In control surface actuator assemblies and flap track mechanisms, thermoset tubes insulate actuator rods from structure to prevent stray current paths that could interfere with corrosion protection systems.

More related guides

Materials

• G10 Material Hub
• Phenolic-Glass-Silicone (G7) Material Hub

Applications

• Motor Insulation Materials
• High-Voltage Standoff Materials
• Coil Form Materials