Ultem PEI Properties — Thermal, Mechanical & Electrical

Ultem (polyetherimide, PEI) delivers a combination of thermal stability, mechanical strength, electrical insulation, and inherent flame retardancy that few thermoplastics match below the price point of PEEK. This page documents property data for Ultem 1000 (unfilled) and Ultem 2300 (30% glass-filled)—the two grades most commonly stocked in sheet, rod, and tube form—with supplemental data on the 2200 (20% glass) variant and notes on the carbon-fiber-filled grade. All values reflect SABIC datasheet figures unless otherwise noted; confirm lot-specific data with your material supplier before design sign-off.

At a glance:

• Continuous-use temperature 340°F (171°C); Tg 419°F (215°C)—much higher than nylon, acetal, or polycarbonate
• Tensile strength 15,000–25,000 psi depending on grade
• Dielectric strength 710 V/mil; dielectric constant 3.15 at 1 MHz (Ultem 1000)
• Inherent UL94 V-0 with no added flame retardant; passes FAR 25.853 vertical burn
• NBS smoke density (Ds at 4 min): < 1.0 (Ultem 1000)—extremely low
• Autoclavable 2,000+ cycles at 270°F (132°C) steam; hydrolytic stability confirmed

Thermal Properties

Continuous-Use Temperature and Heat Deflection

Ultem 1000 carries a continuous service temperature of 340°F (171°C) under moderate load conditions. This is defined as the upper limit for sustained mechanical service without significant creep, dimensional shift, or oxidative degradation—not a peak exposure limit. The glass transition temperature (Tg) of 419°F (215°C) marks the onset of chain mobility; parts should never approach that temperature in service.

The heat deflection temperature (HDT) at 264 psi fiber stress is 410°F (210°C) for Ultem 1000—meaning it retains shape under light structural load to temperatures well above its rated continuous-use figure, a characteristic useful when parts must survive brief thermal excursions during autoclaving, soldering reflow bake-out, or process cleaning.

Coefficient of Thermal Expansion

The coefficient of linear thermal expansion (CLTE) of Ultem 1000 at 31 × 10⁻⁶ in/in/°F is moderate for a thermoplastic. Glass-filling cuts this substantially—Ultem 2300 at 14 × 10⁻⁶ is closer to aluminum (13 × 10⁻⁶), which simplifies the design of metal-plastic assemblies subject to thermal cycling.

Autoclave and Steam Stability

Ultem's hydrolytic stability distinguishes it from many other amorphous thermoplastics. At 270°F (132°C) saturated steam—the standard gravity-cycle autoclave protocol—Ultem 1000 does not exhibit hydrolytic chain scission at the rates seen in polycarbonate, PET, or standard nylon. SABIC-published data validates 2,000+ cycles with less than 2% property retention loss, making it a trusted choice for reusable medical device components. PPSU (Radel) competes directly on this metric; see the Ultem comparisons page for a direct assessment.

Mechanical Properties

Tensile and Flexural

Ultem 1000 (unfilled) achieves 15,000 psi tensile strength at room temperature—roughly 50% above nylon 6/6 and comparable to many aluminum alloy grades on a weight-normalized basis. The 30% glass-filled Ultem 2300 pushes tensile to 25,000 psi and raises flexural modulus from 480,000 psi (unfilled) to 1,200,000 psi. That stiffness gain comes at a cost in elongation-at-break—dropping from ~60% (1000) to ~3% (2300)—so glass-filled grades are brittle and not appropriate for applications requiring snap-fit deflection or impact absorption.

Impact Strength

Notched Izod impact for Ultem 1000 is 1.0 ft-lb/in—lower than polycarbonate (12–17 ft-lb/in) and lower than unfilled PEEK (~1.3 ft-lb/in). Ultem is a relatively brittle amorphous material; sharp corners, sudden wall thickness changes, and residual stress concentrations from machining or injection molding are primary fracture initiators. Design with generous corner radii (≥ 0.031") and avoid press-fit assemblies that create sustained hoop stress.

Hardness and Creep

Rockwell M hardness is 109 for Ultem 1000—harder than most engineering thermoplastics. Creep resistance at elevated temperature is one of Ultem's strongest attributes: at 300°F and 3,000 psi applied stress, creep deformation over 1,000 hours is substantially lower than nylon or polycarbonate at the same conditions, though PEEK outperforms it at temperatures above 340°F.

Electrical Properties

Ultem is a premier electrical insulating thermoplastic. Its dielectric properties are stable across a wide frequency range and hold up at elevated temperatures where lower-performance plastics degrade.

The dielectric constant of 3.15 at 1 MHz is low and stable—a significant advantage in high-frequency signal integrity applications compared to nylon (3.8–4.5) or polysulfone (3.5). Volume resistivity of 10¹⁷ Ω·cm is among the highest measured for any thermoplastic. These properties make Ultem a first-choice insulator for connector housings, coil forms, high-voltage standoffs, and printed circuit board fixtures.

Flammability Properties

UL94 V-0

All standard Ultem grades carry a UL94 V-0 flame rating without addition of halogenated or non-halogenated flame-retardant compounds. V-0 is the most stringent UL94 classification. Because the flame retardancy is inherent—not additive—it does not diminish over time or migrate out of the part. This also simplifies recycling and end-of-life compliance compared to FR-compounded materials.

FAR 25.853 — Aircraft Interior Flammability

Federal Aviation Regulation (FAR) 25.853 defines the flammability test requirements for materials used in aircraft cabin interiors. Ultem passes the 60-second vertical burn test (FAR 25.853(a), Appendix F, Part I) that is required for cabin sidewalls, overhead compartments, and other interior components. This is why Ultem is the dominant plastic in aircraft seat-back hardware, tray tables, PSU bezels, and comparable parts. For regulatory detail on which test methods apply to which component locations, consult your OEM's material requirements document (MRD).

NBS Smoke Density

NBS (NIST) smoke density chamber testing per ASTM E662 measures the concentration of smoke produced during both flaming and non-flaming combustion. Ultem 1000 produces a specific optical density (Ds) at 4 minutes of less than 1.0 in flaming mode—one of the lowest values for any structural thermoplastic. Low smoke density is a critical safety parameter for enclosed spaces such as aircraft cabins and transit vehicles.

Chemical Resistance

Ultem's amorphous structure limits its chemical resistance relative to semicrystalline alternatives like PEEK or PPS. Its resistance profile:

The chemical resistance profile of PEEK is substantially broader, particularly for aggressive solvents and concentrated acids. For a service environment involving prolonged exposure to anything stronger than mild alcohols or dilute acids, evaluate PEEK or PPS (Ryton) before committing to Ultem.

Water Absorption

Ultem absorbs about 0.25% water by weight over 24-hour immersion (ASTM D570). This is low compared to nylon (1.5–9%) but measurable compared to PTFE or PPS (<0.05%). For precision-tolerance parts in humid environments, account for dimensional change—approximately 0.002–0.003 in/in for a fully saturated 1" cross-section. Electrical properties also shift slightly with absorbed moisture; test dielectric constant and dissipation factor under service conditions if tight tolerances are required.

More related guides

Cross-cluster suggestions to help shoppers and engineers explore adjacent topics:

Applications

• Gears
• Electrical Insulation
• Aerospace Interior

Industries

• Aerospace
• Medical

Compare to other materials

• Peek Vs. Ultem Pei
• Ultem Vs. Polycarbonate
• Ultem Vs. Polysulfone

Frequently asked questions — Ultem Pei FAQ