Ultem Plastic — PEI Sheet, Rod & Tube Material Guide

Ultem (polyetherimide, or PEI) is a high-performance amorphous thermoplastic manufactured by SABIC that delivers continuous-use service to 340°F (171°C), inherent UL94 V-0 flammability without added flame-retardant compounds, and exceptional dielectric properties—all in a transparent amber stock that machines cleanly when handled correctly. Engineers specify Ultem across aerospace interiors, medical sterilization equipment, electrical connectors, and semiconductor wafer carriers when the job demands more than standard engineering plastics can provide.

At a glance:

• Continuous-use temperature: 340°F (171°C); glass transition Tg 419°F (215°C)
• Inherent UL94 V-0 flame rating—no FR additive required
• Meets FAR 25.853 aircraft interior flammability requirements
• Autoclavable 2,000+ steam sterilization cycles without hydrolytic degradation
• Tensile strength 15,000 psi (Ultem 1000) up to 25,000 psi (Ultem 2300 glass-filled)
• Available as sheet, rod, and tube in natural amber and black
• Grades: Ultem 1000 (unfilled), 2300 (30% GF), 2200 (20% GF), GF30, CF (carbon fiber)

What Is Ultem / PEI?

Polyetherimide was commercialized by General Electric Plastics in 1982 under the Ultem trade name. SABIC acquired the brand and continues to manufacture it under the same name. The "PEI" designation refers to the polymer chemistry—ether and imide linkages along the backbone—which produces the combination of high heat resistance, rigidity, and inherent flame retardancy that defines the family.

Within the high-performance thermoplastic tier, Ultem occupies a specific and well-defined niche. It outperforms standard engineering plastics—acetal, nylon, polycarbonate—on heat resistance, flammability, and dielectric properties by a wide margin. It falls below PEEK and Torlon on continuous-use temperature, chemical resistance, and fracture toughness. That positioning, combined with a price point roughly 30–50% below PEEK, makes Ultem the first material engineers reach for when standard plastics fail temperature or flammability requirements but PEEK is cost-prohibitive or over-specified.

As generic polyetherimide (PEI), the same base polymer chemistry is also produced by other manufacturers outside the SABIC Ultem family. However, Ultem remains the dominant trade name in North American distribution, and when engineers specify "Ultem" they typically mean SABIC-origin PEI to the ASTM D5205 standard.

Amorphous vs. Semicrystalline

Ultem is amorphous, not semicrystalline. That distinction matters for machining and chemical resistance. Unlike PEEK—which is semicrystalline and offers broader solvent resistance—Ultem is attacked by chlorinated solvents and strong acids. However, its amorphous structure means it can be bonded with solvents and adhesives more easily than PEEK, and optical transparency is achievable in the unfilled grade. See the Ultem vs PEEK comparison guide for a full property-by-property breakdown.

The Amber Color

Natural Ultem is transparent amber—a product of the imide chemistry, not a pigment or dye. Black Ultem uses a carbon-black colorant. The amber transparency is not optical-grade clarity (it is not intended as a glazing material), but it is distinctive and allows visual inspection of part wall sections.

Amorphous Structure: Implications for Design and Processing

Ultem's amorphous polymer structure means it has no defined melt point—instead it softens progressively above its Tg of 419°F. This produces excellent dimensional stability up to the Tg, but also means Ultem is more notch-sensitive and stress-crack-prone than semicrystalline materials like PEEK or PPS. Residual stresses from extrusion or machining can produce delayed cracking in service, especially when the part contacts even mildly aggressive solvents. Annealing before machining—and again after machining for precision or load-bearing parts—is the standard mitigation.

The amorphous structure also simplifies bonding: Ultem can be solvent-cemented with methylene chloride or NMP-based cements, and ultrasonic welding produces consistent results with standard energy directors. Semicrystalline plastics are typically more difficult to bond.

Ultem Property Highlights

For complete data tables including thermal conductivity, coefficient of thermal expansion, and dielectric constant by frequency, see the full Ultem properties data.

Grades Overview

SABIC produces Ultem in several formulations. The two most stocked in plastic distribution are Ultem 1000 (unfilled) and Ultem 2300 (30% glass fiber). Additional grades serve specialized structural and electrical applications.

Glass-filled grades are not transparent and add abrasiveness that increases tool wear during machining. The grades comparison page covers selection criteria in detail.

Key Applications

Aerospace Interior Components

Ultem meets FAR 25.853 aircraft cabin flammability requirements inherently—no FR additive compounds the mechanical properties or adds regulatory uncertainty. Seat components, overhead bin brackets, galley fittings, air ducting inserts, and lighting bezels are all common applications. Low smoke density (NBS smoke chamber) reinforces its suitability where passenger safety regulations apply.

Medical Sterilization

Ultem withstands 270°F (132°C) saturated steam autoclave cycles—the standard hospital sterilization protocol—without significant dimensional change, surface crazing, or hydrolytic degradation. Validated to 2,000+ cycles in published SABIC testing, it is used for surgical instrument trays, endoscope components, dental tool handles, and reusable cassette fixtures. Ultem 1000 carries USP Class VI biocompatibility and FDA 21 CFR 177.1595 compliance. Full compliance details appear in the FDA and compliance guide.

Electrical Connectors and Insulators

With a dielectric strength of 710 V/mil and a dielectric constant of 3.15 at 1 MHz, Ultem outperforms most engineering thermoplastics in electrical isolation applications. Its UL94 V-0 rating requires no added flame retardant. Connector housings, insulating standoffs, coil bobbins, and terminal blocks running in elevated-temperature environments—where nylon or acetal would creep or degrade—are natural fits.

Semiconductor Wafer Carriers

Ultem's dimensional stability at process temperatures, its cleanroom-compatible outgassing profile, and its chemical resistance to the alkaline and mild acid rinses used in wafer processing make it a recognized material for wafer carriers, end-effectors, and cassette trays. Carbon-fiber-filled grades add static dissipation where ESD protection is required.

Available Forms and Stock Sizes

Ultem sheet, rod, and tube are stocked in both natural amber and black. Standard sheet runs from 12" × 24" up to 24" × 48" in thicknesses from 0.062" through 2.0". Rod diameters range from 1/4" through 6". Tube is available in select OD/ID combinations for applications requiring bore dimensions without full-stock drilling.

For complete size availability and thickness/diameter increments, see the specifications page.

Machining Ultem

Ultem is machinable with standard CNC equipment, but its amorphous structure makes it more notch-sensitive and stress-prone than semicrystalline materials. Key rules: anneal stock before machining to relieve molding or extrusion stresses, use sharp carbide tooling, keep feed rates light, and take finishing passes of 0.005" or less. Avoid chlorinated cutting fluids—they attack Ultem. Compressed air or water-soluble coolants are acceptable.

Machined parts with sharp internal corners or thin walls are vulnerable to stress cracking in service if residual machining stresses are not managed. A post-machining stress-relief anneal at 340°F for 1–4 hours (depending on cross-section) reduces this risk. Full machining protocols are in the Ultem machining guide.

Ultem vs. Competing Materials

The three most common comparison questions received from engineers and buyers:

Ultem vs. PEEK — PEEK offers a higher continuous-use temperature (480°F vs. 340°F), semicrystalline structure with better chemical resistance, and higher fracture toughness. Ultem costs roughly 30–50% less per pound in unfilled stock and has inherently better flame/smoke performance for cabin applications. The detailed head-to-head is at PEEK vs. Ultem PEI.

Ultem vs. Polycarbonate — PC is cheaper and optically clearer but limited to 240°F continuous, carries only a UL94 V-2 base rating, and cannot withstand autoclave sterilization. Ultem is the correct answer when temperature, flame, or sterilization requirements disqualify polycarbonate.

Ultem vs. Polysulfone / PPSU — Polysulfone (PSU, PPSU) is a direct amber-colored competitor with a lower price point and similar autoclave capability in PPSU form (Radel), but its tensile and stiffness numbers fall below Ultem at elevated temperature. PPSU is rated to 350°F continuous; Ultem 1000 at 340°F is comparable, but Ultem's superior modulus at temperature gives it an edge in load-bearing applications. Full comparison on the Ultem comparisons page.

Frequently Asked Questions

Why is Ultem amber-colored? The amber color is inherent to the PEI chemistry—specifically the imide groups in the backbone—not a dye or additive. It is consistent across production lots and grades.

Can Ultem be used outdoors? Ultem has limited UV resistance. Extended outdoor exposure causes surface yellowing and surface degradation. For UV-stable applications, consider a UV-stabilized alternative.

Is Ultem FDA-approved for food contact? Ultem 1000 meets FDA 21 CFR 177.1595 for repeated food contact use and USP Class VI biocompatibility. See the FDA compliance page.

For 12 more questions answered by our materials engineers, see the Ultem FAQ.

Regulatory and Compliance Summary

Ultem 1000 satisfies the compliance needs of three major regulated industries without reformulation or special compound:

Aerospace: FAR 25.853 aircraft interior vertical burn test; low NBS smoke density (Ds < 1.0 at 4 minutes, flaming mode); UL94 V-0. These properties are inherent to the base polymer and do not require documentation of FR additive supply chain.

Medical and food contact: FDA 21 CFR 177.1595 (polyetherimide resins) for food-contact use; USP Class VI biocompatibility; NSF-listed for potable water. Validated autoclave sterilization to 2,000+ cycles at 270°F steam.

Electrical safety: UL94 V-0; dielectric strength 710 V/mil; arc resistance 128 seconds. All standard stocked grades carry the V-0 rating.

For purchasing and documentation requirements, the FDA compliance page covers what to request from your distributor.

Summary

Ultem PEI occupies a performance tier between standard engineering plastics and ultra-premium materials like PEEK or Torlon. For applications requiring continuous service above 300°F, inherent UL94 V-0 or FAR 25.853 compliance, autoclave sterilizability, and excellent dielectric properties—at a cost well below PEEK—Ultem is a primary candidate. It requires more machining care than acetal or nylon but delivers structural and thermal performance those materials cannot match.

Contact our materials team for grade recommendations, cut-to-size quoting, or tolerance review on your next Ultem component.

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