Aircraft interiors
Seat back panels, tray tables, lavatory hardware, air ducting. The plastic that meets FAR 25.853 cabin flame requirements without coatings.
PolyEtherImide · Amorphous thermoplastic
Ultem (PEI)
Amber transparent high-temperature engineering thermoplastic. Continuous service to 170 °C, dimensionally stable, dielectrically excellent, sterilizable, FDA-approved. Aerospace interior, semiconductor wafer handling, and high-end medical applications.
UTS
105 MPa
Density
1.27 g/cc
Service T
170 °C
Mach.
70 /100
When to use
Pick Ultem when Delrin is too cold and PEEK is too expensive.
Ultem (Sabic’s trade name for polyetherimide) sits between Delrin and PEEK in the engineering plastic hierarchy. It handles 170 °C continuous service (vs Delrin’s 100 °C and PEEK’s 250 °C), has excellent dielectric properties, and is naturally amber-transparent — useful when you want to see fluid flow or component position. It machines comparably to PEEK but costs roughly half.
Three killer features set Ultem apart: FAR 25.853 flame compliance (aircraft cabin interior — pass without coatings), USP Class VI biocompat with autoclavable grades for medical, and low outgassing for vacuum-chamber and semiconductor environments.
Strengths
Why aerospace specifies it.
- Aircraft interior approvedFAR 25.853 (a) flame, smoke, and toxicity compliant without coatings. The plastic in Boeing/Airbus seat backs, wall panels, ducting.
- 170 °C continuous serviceSignificant step up from Delrin (100 °C) or polycarbonate (120 °C). Holds modulus where lesser plastics soften.
- Sterilizable medical gradeUSP Class VI grades approved for autoclave (steam) sterilization. Standard for surgical instrument trays, sterilization racks.
- Excellent dielectricDielectric strength 33 kV/mm. Used in high-voltage insulators, electrical connectors, RF transmissive components.
- Naturally transparent (amber)See-through with a yellow-amber tint. Useful for inspection windows, fluid sight glasses.
- Low outgassing (vacuum compatible)TML <1%. Used in semiconductor wafer handling, satellite components, vacuum chambers.
Trade-offs
Where PEEK or Delrin win.
- Lower chemical resistance than PEEKSusceptible to chlorinated solvents, methylene chloride, hot caustic. PEEK handles much more aggressive chemistry.
- Notch-sensitiveLike other amorphous plastics, Ultem is sensitive to sharp corners and stress concentrations. Use generous fillets.
- Cost vs Delrin$40-60/lb stock — 5-10× Delrin. Justified only when temperature, dielectric, or aerospace cert matters.
- UV degradationYellows further and embrittles in sustained UV. Indoor/internal use only without UV-stabilized grade.
- Lower max strengthUTS 105 MPa. PEEK reinforced grades reach 200+ MPa. For structural plastic, PEEK-CF30 is stronger.
- Stress-cracking riskSolvents and stress combined cause crazing. Anneal stock before high-tolerance machining.
Specs
Mechanical, physical & thermal data.
Properties for Ultem 1000 (unfilled, virgin grade). Reinforced grades and aerospace-cert (Ultem 9085) follow.
Mechanical
Properties (unfilled)
| Tensile strength at yield | 105 MPa (15 ksi) |
|---|---|
| Tensile elongation at yield | 7% |
| Tensile elongation at break | 60% |
| Tensile modulus | 3.2 GPa |
| Flexural strength | 165 MPa |
| Flexural modulus | 3.3 GPa |
| Compressive strength | 140 MPa |
| Hardness (Rockwell) | M109 / R125 |
| Izod impact (notched) | 53 J/m |
Source: Sabic Ultem 1000 datasheet. GF30 (30% glass): UTS 175 MPa, modulus 9 GPa. Ultem 9085: aerospace flame-cert variant.
Thermal
Temperature performance
| Glass transition (Tg) | 217 °C |
|---|---|
| Continuous service | 170 °C (340 °F) |
| HDT (1.8 MPa) | 200 °C |
| HDT with GF30 | 210 °C |
| CTE (–40 to 150 °C) | 47 µm/m·°C |
| Thermal conductivity | 0.22 W/m·K |
| UL94 flammability Self-extinguishing | V-0 |
| FAR 25.853 Aircraft interior | Pass |
One of very few plastics to meet FAR 25.853 cabin flame-smoke-toxicity without protective coating.
Physical & electrical
At room temperature
| Density | 1.27 g/cc (0.0459 lb/in³) |
|---|---|
| Water absorption (24 hr) | 0.25% |
| Dielectric strength | 33 kV/mm |
| Dielectric constant (1 kHz) | 3.15 |
| Volume resistivity | >10¹⁷ Ω·cm |
| Light transmission Amber tint | ~73% |
| FDA / USP VI grades | Available |
| NSF 51 (food contact) | Some grades |
Outgassing total mass loss (TML) for Ultem 1000 is 0.42% — qualifies for most spacecraft applications per ASTM E595.
Grade selection
Pick the right Ultem.
| Grade | UTS | Modulus | Best for |
|---|---|---|---|
| Ultem 1000 (unfilled) | 105 MPa | 3.2 GPa | General machining, transparent applications, electrical |
| Ultem 2300 (GF30 — 30% glass) | 175 MPa | 9.0 GPa | Higher stiffness, dimensional stability |
| Ultem 2400 (GF40) | 190 MPa | 12 GPa | Maximum stiffness, structural plastic |
| Ultem 9085 | 115 MPa | 2.6 GPa | Aircraft interior — FAR 25.853, FST cert |
| Ultem HU1000 (USP VI) | 105 MPa | 3.2 GPa | Sterilizable medical, autoclave, USP Class VI |
| Ultem 1010 (high-flow) | 105 MPa | 3.2 GPa | Thin-wall molded parts; same machined properties |
Specifications
Common purchase specs.
ASTM D5205
Standard for PEI molding/extrusion
FAR 25.853
Aircraft interior flame, smoke, toxicity
USP Class VI
Pharmaceutical contact biocompat (HU grades)
FDA 21 CFR 177.1595
Food contact compliance (some grades)
MIL-DTL-46197
PEI for military applications
ASTM E595
Outgassing (vacuum) compliance
IEC 60695
Flammability and ignition standards
UL94 V-0
Self-extinguishing standard
Machining
How we cut it.
Ultem cuts a lot like PEEK — sharp tools, moderate speeds, generous chip clearance, no coolant that contains chlorinated solvents. Anneal stock before tight-tolerance work to prevent stress-cracking.
Cutting speed
500–800 SFM with carbide on unfilled. GF30 cuts slower — fillers are abrasive.
Feed rate
Aggressive constant feed. Plastic doesn’t work-harden but heat builds with rubbing.
Tooling
Polished carbide for unfilled. Diamond-coated (PCD) for glass-filled grades.
Coolant
Air blast or water-soluble. Avoid chlorinated cutting oils — Ultem can stress-crack.
Anneal first
200 °C for 4 hr before machining for tight-tolerance parts. Reduces residual stress that causes drift.
Sharp edges
Notch-sensitive — round all internal corners (R 0.5 mm minimum) to prevent crack initiation.
Threading
Single-point or roll forms preferred. Cut taps work — sharp HSS or single-flute taps.
Drilling
Slow back out — Ultem can grab drills. Spiral-flute drills with positive geometry.
Applications
Where Ultem shows up.
Semiconductor & vacuum
Wafer-handling end-effectors, vacuum chamber components, plasma etch fixtures. Low outgassing + thermal stability is the niche.
Sterilizable medical
Surgical instrument trays, sterilization racks, tubing manifolds. USP Class VI HU1000 grade survives autoclave cycling.
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