Plastics for Aerospace Interior Parts — PEEK, Ultem, PPS & More

Aircraft cabin and interior components face a unique regulatory environment: every non-metallic material must pass FAA flammability requirements under FAR 25.853, and many interior subassemblies must also meet OSU heat release and NBS smoke density limits. The materials that survive this qualification gauntlet—PEEK, Ultem/PEI, PPS/Ryton, PAI/Torlon, and G7 glass-silicone laminate—each serve distinct structural and thermal roles inside the fuselage. This guide explains the regulatory framework, compares the top candidate materials, and provides selection guidance for both cabin-interior and behind-the-panel structural applications.

TL;DR

• FAR 25.853 governs flammability for cabin interior materials; OSU heat release ≤65 kW·min/m² and ≤65 kW/m² peak are required for most interior panels.
• Ultem/PEI is the most widely qualified thermoplastic for cabin interior structural parts—it achieves FAR 25.853 compliance without halogenated additives.
• PEEK is preferred for high-load structural parts, bearing cages, bushings, and fastener components exposed to elevated temperature or aggressive fluids.
• PPS/Ryton offers an excellent cost-to-performance ratio for non-structural brackets, clips, and conduit supports that need chemical resistance and UL94 V-0.
• PAI/Torlon is specified for the most demanding structural inserts, wear pads, and bearing races at temperatures where other thermoplastics soften.
• G7 glass-silicone laminate (NEMA grade) is used for electrical insulation panels, terminal supports, and wave-guide brackets where flame resistance at high temperature is required.
• Interior cabin plastics and behind-the-panel structural plastics have different qualification paths—confirm which section of FAR 25.853 applies.

FAA Flammability Framework — What the Regulations Require

Before selecting a material, engineers must understand which regulatory tests apply to their specific component. FAR 25.853 is not a single test—it is a collection of test methods applied based on where the material is located in the aircraft and how large the component is.

FAR 25.853(a) — Vertical Burn Test

The 60-second vertical burn test (Appendix F, Part I, paragraph (a)(1)) applies to materials in the cabin interior. The material must self-extinguish within 15 seconds after the ignition source is removed, and the burned length must be ≤6 inches. Most PEEK, Ultem, PPS, and PAI grades pass without modification.

OSU Heat Release — 2-Minute and Peak

For large-area interior components (walls, ceilings, partitions, galleys, overhead bins—areas ≥1 ft²), FAR 25.853(d) requires the Ohio State University (OSU) heat release test. Two limits apply:

• 2-minute integrated heat release: ≤65 kW·min/m²
• Peak heat release rate: ≤65 kW/m²

Ultem/PEI in standard unfilled grades typically achieves 30–50 kW·min/m² and 30–50 kW/m²—comfortably within limits. Always request OSU test data from the material supplier for the specific grade and thickness being qualified.

NBS Smoke Density — Ds(4)

The NBS smoke chamber test (ASTM E662) is referenced for many interior applications. The required maximum Ds(4) at 4 minutes varies by application but is commonly ≤200 in flaming mode. PEEK, Ultem, and PPS all achieve low smoke density in unfilled grades.

PEEK — High-Load Structural Aerospace Plastic

PEEK is the engineering thermoplastic benchmark for aerospace structural applications requiring sustained service above 300°F (149°C), combined resistance to Skydrol hydraulic fluid, aviation fuel, and cleaning agents, and high fatigue resistance under cyclic load. It is used in bearing cages, bushing retainers, fastener insulators, actuation system components, and instrument-housing brackets.

Compliance and Certification

Natural (unfilled) PEEK and carbon-fiber-filled PEEK grades are available with FAR 25.853 OSU heat release test data. Glass-filled PEEK also qualifies, though glass-filled grades have slightly higher Dk values—relevant for components near antennas or RF systems. Request qualification test reports (OSU, vertical burn, smoke) from the distributor.

Cabin vs. Structural PEEK Applications

Behind-the-panel structural PEEK (frames, brackets, fluid-system components) is subject to different qualification requirements than visible cabin interior components. Structural parts may only need the vertical burn test; visible interior panels require OSU heat release data. Confirm with your DER (Designated Engineering Representative) which tests apply to each component.

Machining for Aerospace Tolerances

PEEK machines to tight tolerances (±0.001"–0.002") with sharp carbide tooling. Chip control is important—PEEK produces long, stringy chips that can re-cut the surface. Use through-coolant or compressed air and positive-rake end mills. Review the PEEK machining guide for speeds, feeds, and annealing recommendations for stress-relieved parts.

Ultem/PEI — The Cabin Interior Standard

Ultem polyetherimide is the single most widely used thermoplastic in commercial aircraft cabin interiors. Its inherent flame resistance (UL94 V-0 at 0.010" without flame-retardant additives) and consistent OSU heat release performance make it the default choice for:

• Seat components (armrests, seat backs, buckle housings)
• Overhead bin latches and structural brackets
• Galley components and trolley guides
• Lighting bezels, air nozzle bodies, and reading light housings
• Interior panel clips, standoffs, and fastener inserts

Ultem 1010 vs. 2300

Ultem 1010 (unfilled) is the baseline for most interior applications—maximum temperature capability (340°F / 171°C), good impact resistance, and the best surface finish for visible components.

Ultem 2300 (30% glass-filled) provides 50% higher flexural modulus, useful for load-bearing brackets and clips. It still achieves V-0 and FAR 25.853, though surface finish is rougher.

Both grades are available in rod and sheet for machined prototypes and low-volume parts, and both are injection-moldable for production.

Comparison with PEEK

Ultem is approximately 30–40% lower cost than PEEK and processes at lower temperatures (lower tooling cost for injection molding). PEEK is chosen when service temperature exceeds 340°F (171°C) or when chemical exposure to Skydrol or strong solvents is expected. See the PEEK vs. Ultem/PEI head-to-head comparison for a detailed breakdown.

PPS/Ryton — Cost-Effective Behind-Panel Plastic

Polyphenylene sulfide (PPS, sold as Ryton® by Solvay) offers an excellent combination of chemical resistance, dimensional stability, and inherent flame resistance at a cost point below PEEK and Ultem. It is UL94 V-0 in unfilled form and achieves FAR 25.853 vertical burn compliance in qualified grades. Maximum continuous service temperature is 428°F (220°C).

Applications in Aircraft

PPS is used primarily for non-structural and lightly loaded components behind the cabin panel:

• Conduit clips and cable harness supports
• Fluid connector brackets and retaining clips
• EMI shielding inserts
• Hydraulic line standoffs

Chemical Resistance Advantage

PPS resists virtually all aircraft fluids—Skydrol hydraulic fluid, aviation fuel, MEK, and strong acids and bases—better than nylon, acetal, or even Ultem. For components in the wheel well, engine bay, or hydraulic system routing areas that also need flame compliance, PPS is often the best cost-performance choice.

Filled Grades

40% glass-filled PPS is the most common structural grade, with tensile strength to 21,000 psi and flexural modulus to 1.6 × 10⁶ psi. Carbon-filled grades are also available for lower thermal expansion and higher stiffness. See the PPS/Ryton material hub for filled grade data.

PAI/Torlon — Maximum Performance for Critical Inserts

Polyamide-imide (PAI, sold as Torlon® by Solvay) is the highest-performing melt-processable thermoplastic available. With tensile strength to 27,000 psi, a compressive strength of 45,000 psi, and a maximum service temperature of 500°F (260°C), Torlon is specified for the most demanding aerospace applications:

• Fastener bushings and insert sleeves in structural airframe joints
• Wear pads in control surface actuation systems
• Bearing cages in high-temperature gearboxes
• High-load anti-rotation pins and structural inserts

FAR 25.853 Compliance

Torlon grades are available with FAR 25.853 vertical burn compliance. OSU heat release data is available from the manufacturer for specific grades and thicknesses. As with PEEK, request grade- and thickness-specific test reports.

Machining Considerations

Torlon is more difficult to machine than PEEK or Ultem—it is harder, more abrasive, and requires sharp tooling. Parts are typically stress-relieved after rough machining and again before final machining to remove residual thermal stress from curing. Review the PAI/Torlon material hub for full machining protocol.

G7 Glass-Silicone Laminate — Electrical Insulation in Aircraft

G7 (NEMA grade glass-silicone laminate) provides the highest continuous service temperature of any standard laminate—428°F (220°C)—with excellent dielectric properties and UL94 V-0 flame resistance. In aircraft, it is used for:

• High-voltage insulation panels behind the avionics bay
• RF waveguide and antenna feed structural brackets
• Terminal board and bus bar supports in power distribution centers
• Motor slot liners in cabin air compressors

G7's silicone resin binder does not produce chlorinated combustion products, making it acceptable in enclosed cabin spaces. Review the glass-silicone phenolic hub for NEMA grade specifications and available thicknesses.

How to Choose — Decision Matrix

Is the component in the visible cabin interior (≥1 ft²)?

• Yes → OSU heat release test data required; Ultem/PEI is the default; confirm grade-specific OSU data.
• No (structural, behind-panel) → Vertical burn test only; PEEK, PPS, or Torlon depending on load and temperature.

Maximum service temperature:

• ≤340°F (171°C) → Ultem/PEI covers most cabin applications.
• ≤428°F (220°C) → PPS/Ryton or G7 for electrical insulation.
• ≤480°F (249°C) → PEEK.
• ≤500°F (260°C) → PAI/Torlon.

Mechanical load:

• Lightly loaded brackets, clips → PPS/Ryton (lowest cost of compliant options).
• Moderate structural → Ultem 2300 (glass-filled) or PEEK.
• High-stress inserts, bearing races → PAI/Torlon.

Chemical exposure:

• Skydrol, strong solvents → PEEK or PPS (Ultem has moderate Skydrol resistance; verify with the manufacturer).
• Cleaning agents, mild solvents → Ultem is adequate.

Electrical insulation function:

• High-temperature insulation panels → G7.
• Structural insulation with moderate temperature → Ultem or G10 and FR4.

Sizes & Forms Commonly Stocked

Spec Sheet & Test Data

• PEEK Material Hub — Properties, Machining & Grades
• Ultem/PEI Material Hub
• PPS/Ryton Material Hub
• PAI/Torlon Material Hub
• Glass-Silicone G7 Material Hub

Need aerospace-grade plastic with FAR 25.853 test reports? FedMat stocks PEEK, Ultem, PPS, and Torlon with manufacturer-supplied OSU, vertical burn, and smoke data available on request.

More related guides

Cross-cluster suggestions for engineers and buyers planning this application:

Materials

• Phenolic Glass Silicone hub
• Pps Ryton hub
• Ultem Pei hub
• Peek hub
• Pai Torlon hub

Industries

• Aerospace
• Medical
• Semiconductor

Material comparisons

• Peek Vs. Ultem Pei
• Peek Vs. Pai Torlon
• Pps Vs. Peek

Forms commonly used

• Plastic sheet stock
• Plastic rod stock