Ultem PEI in Aerospace: Meeting FAR 25.853 & Lightweighting Demands
| May 27, 2026
1. Introduction Ultem PEI in Aerospace
The aerospace industry faces a constant challenge: reduce aircraft weight to improve fuel efficiency while maintaining the highest safety standards. Every kilogram saved on an aircraft can save hundreds of gallons of fuel per year. At the same time, materials used in cabin interiors must be flame‑resistant, produce low smoke and toxicity, and withstand repeated cleaning and temperature fluctuations.
Ultem™ PEI (polyetherimide) from SABIC has emerged as a go‑to engineering plastic for these demanding requirements. Its unique combination of high strength‑to‑weight ratio, inherent flame retardancy, and excellent thermal stability makes it ideal for a wide range of aerospace components – from seat backs to ducting and electrical connectors.
In this guide, we’ll explore why Ultem PEI is so widely adopted in aerospace, key applications, a real‑world case study, processing tips, and how CISKO NEW MATERIAL supports your compliance needs.
2. Why Ultem PEI for Aerospace?
Ultem PEI (grades like 1000, 1010, 2100, 2200, 2300, 2400) offers several properties that directly address aerospace requirements.
2.1 High Strength‑to‑Weight Ratio
Aircraft designers seek materials that are stiff and strong but lightweight. Ultem PEI has a specific gravity of only 1.27 (unfilled) to 1.61 (40% glass filled). Its tensile strength ranges from 110 MPa to over 180 MPa, providing a strength‑to‑weight ratio comparable to many metals.
Example: Replacing an aluminium bracket (density 2.7 g/cm³) with Ultem 2300 (density 1.51 g/cm³) can reduce part weight by about 44%.
2.2 Inherent Flame Retardancy – No Halogens Needed
Unlike many plastics that require additive flame retardants (some of which are being restricted under PFAS regulations), Ultem PEI is inherently flame retardant. It achieves UL94 V‑0 ratings at thicknesses as low as 0.75 mm (Ultem 1000) and even 0.25 mm for glass‑filled grades (Ultem 2300). For high‑impact areas, it also offers UL94 5VA ratings.
This is crucial for compliance with FAR 25.853 (Federal Aviation Regulations for aircraft interior materials).
2.3 Low Smoke and Toxicity (FAR 25.853 Appendix F, Part V)
When a fire occurs in an aircraft cabin, toxic smoke is the primary killer. FAR 25.853 Appendix F, Part V (the “OSU” test) measures heat release and smoke density. Ultem PEI has an oxygen index (LOI) of 44–50%, meaning it resists ignition and produces very little smoke. The NBS smoke density (Ds) at 4 minutes is below 2 – well within the required limits.
2.4 Long‑Term Thermal Stability (RTI 170°C)
Under‑hood and interior components may see sustained temperatures of 150–170°C. Ultem PEI has a Relative Thermal Index (RTI) of 170°C for electrical and mechanical properties (UL 746B). Its glass transition temperature (Tg) is 217°C, so it retains stiffness far above the operating range.
2.5 Chemical and Hydrolytic Resistance
Aircraft interiors are regularly cleaned with harsh chemicals. Ultem PEI resists many solvents, de‑icing fluids, and cleaning agents. It also has good hydrolytic stability, surviving repeated steam cleaning or humidity exposure without losing properties.
3. Key Aerospace Applications
Ultem PEI is used in both structural and non‑structural aircraft components. Below are the most common applications, with recommended grades.
| Application | Recommended Ultem Grade | Why This Grade |
|---|---|---|
| Cabin interior panels | 1000, 1010 | Smooth surface, transparent amber option, easy to paint |
| Seat back shells | 2300 (30% glass) | Highest stiffness, very thin walls possible, 0.25mm V0 |
| Armrests and tray tables | 2200 (20% glass) | Good balance of stiffness and impact resistance |
| Galley inserts | 1000, 1010 | Food contact compliant (some grades), FDA available |
| Air ducting | 1000 | Lightweight, good creep resistance at 150°C |
| Electrical connectors | 2100, 2200 | High dielectric strength, stable at high frequency |
| Junction boxes | 2400 (40% glass) | Maximum stiffness for structural enclosures |
| Brackets & clips | 2300, 2400 | Metal replacement, high HDT (210°C) |
| Wire insulation | 1285 (flexible blend) | FDA compliant, transparent |
3.1 Cabin Interior Panels
Wall panels, ceiling panels, and luggage bin components benefit from Ultem 1000’s excellent surface finish and low smoke emissions. The natural amber colour can be painted or used as a decorative accent.
3.2 Seat Back Shells and Armrests
Aircraft seats require thin, stiff shells to maximise passenger space. Ultem 2300 (30% glass filled) can be moulded to wall thicknesses of 1.5–2.0 mm, providing a strong, flame‑resistant shell that easily passes the 12‑second vertical burn test.
3.3 Ducting and Air Management
Hot air from engines and auxiliary power units is routed through ducts that must withstand 150–180°C. Ultem 1000 is often blow‑moulded or injection moulded into complex duct shapes, thanks to its high HDT and dimensional stability.
3.4 Electrical Connectors and Junction Boxes
Avionics and wiring systems require connectors that won’t degrade at high temperatures. Ultem 2100 (10% glass) offers good flow for pin‑dense connectors, while Ultem 2200 provides extra stiffness for larger housings. The high dielectric strength (28 kV/mm) ensures signal integrity.
4. Case Example
Background: An aerospace tier‑1 supplier was tasked with redesigning a seat mounting bracket. The original bracket was machined from 6061 aluminium. The goals were:
- Reduce weight by at least 40%
- Maintain or exceed strength
- Pass FAR 25.853 vertical burn test (12 seconds self‑extinguishing)
- Achieve cost reduction through injection moulding
Solution: The engineering team selected Ultem 2300 (30% glass fibre reinforced).
Results:
| Metric | Aluminium 6061 | Ultem 2300 | Change |
|---|---|---|---|
| Weight (per part) | 120 g | 66 g | -45% |
| Tensile strength | 310 MPa | 175 MPa | Lower, but sufficient |
| Flexural modulus | 69 GPa | 9.4 GPa | Lower, but part geometry compensated |
| Flammability | Non‑flammable | V0 at 0.25 mm | Passed |
| Production method | CNC machining | Injection moulding | -60% part cost |
The bracket passed the 12‑second vertical burn test with zero after‑flame. The moulded part also simplified assembly because integral snap‑fits could be added. The customer approved the design and ordered 50,000 units per year.
Key takeaway: Ultem 2300 is not just a direct replacement; it enables design consolidation and lower part cost while meeting strict flame safety requirements.
5. Processing Considerations for Aerospace Parts
Injection moulding Ultem PEI for aerospace applications requires careful attention to processing parameters. Below are critical guidelines.
5.1 Drying – The Most Important Step
Ultem PEI is hygroscopic. If not properly dried, moisture causes splay, voids, and hydrolytic degradation.
- Drying temperature: 150°C (302°F)
- Drying time: 4–6 hours (up to 24 hours cumulative)
- Dew point: −40°C or lower (desiccant dryer recommended)
- Maximum moisture content before moulding: 0.02%
Tip: Use a hopper dryer or dehumidifying dryer. Do not use an open oven – it may not reach low enough dew point.
5.2 Injection Moulding Parameters
| Parameter | Typical Range |
|---|---|
| Melt temperature (rear to nozzle) | 330–410°C (grade dependent) |
| Mold temperature | 135–180°C |
| Injection pressure | 600–1000 kg/cm² |
| Back pressure | 0.3–0.7 MPa |
| Screw speed | 40–70 rpm |
| Vent depth | 0.025–0.076 mm |
For glass‑filled grades (2100, 2200, 2300, 2400): Use a higher melt temperature (350–400°C) and ensure mold steel is abrasion‑resistant (e.g., tool steel with hardness >55 HRC).
5.3 Post‑Molding Annealing
Although not always required, annealing can relieve internal stresses, especially for thick parts or parts with metal inserts.
- Annealing temperature: 150°C for 2–4 hours (in air circulating oven)
- Cooling: Slow cool to room temperature (1–2 hours)
Annealing improves dimensional stability and reduces the risk of crazing under load.
5.4 Quality Control for Aerospace
Aerospace parts require full traceability. CISKO NEW MATERIAL provides:
- COA (Certificate of Analysis) for each batch
- SDS (Safety Data Sheet) and TDS (Technical Data Sheet)
- UL Yellow Card for relevant grades (e.g., E121562 series)
- REACH / RoHS declarations on request
We recommend that molders perform incoming moisture analysis and run periodic test bars to verify mechanical properties.
6. Regulatory Support from CISKO NEW MATERIAL
At CISKO NEW MATERIAL, we understand that aerospace compliance is non‑negotiable. As an authorised distributor of SABIC Ultem PEI, we provide:
- Full FAR 25.853 test data (heat release, smoke density, vertical burn)
- UL Yellow Cards with HWI, HAI, CTI, and RTI values
- Batch‑specific COAs for full traceability
- REACH, RoHS, and conflict mineral declarations
We also offer technical support to help you select the right grade and optimise your moulding process. If you are qualifying a new material for an aerospace program, we can supply sample quantities (as low as 1 kg) with full documentation.
7. Conclusion & Call to Action
Ultem PEI is a proven, reliable material for aerospace interior and under‑hood applications. Its unique combination of lightweight, inherent flame retardancy (FAR 25.853 compliance), low smoke, and high thermal stability makes it an excellent choice for seat components, ducting, connectors, and structural brackets.
Key takeaways:
- Ultem 1000 / 1010 for unreinforced, transparent or high‑flow needs
- Ultem 2300 (30% glass) for maximum stiffness and thin‑wall moulding
- Strict drying and proper moulding parameters are essential for defect‑free parts
- CISKO provides full compliance documentation and technical support
Ready to explore Ultem PEI for your aerospace project?
📧 Contact our engineering team: info@pp-pei.com
📞 Call us: +86 13538114678
🌐 Browse our Ultem PEI product range: Shop Ultem PEI
Request a sample or a compliance package today.
