Ultem (PEI)

Overview

Ultem is the trade name for Polyetherimide (PEI), an amorphous high-performance thermoplastic. It occupies a middle tier in the high-performance plastics spectrum — above engineering grades like ABS and nylon, but typically below PEEK in maximum service temperature. Its amber colour and high stiffness make it recognisable. Ultem is valued for its combination of high-temperature capability, inherent flame resistance without additives, good dimensional stability, and broad chemical resistance. It is used extensively in aerospace, medical device, semiconductor, and food processing equipment applications. Unfilled, glass-filled, and carbon-filled grades are available, each with different mechanical and thermal properties.

Working properties

• High continuous service temperature

  Ultem maintains structural integrity and stiffness at elevated temperatures well above most engineering thermoplastics. It can withstand repeated steam sterilisation cycles — a key reason for its use in reusable medical instrument components. Confirm the specific grade and intended cycle conditions before relying on this property.

• Inherent flame resistance

  PEI is inherently flame-resistant without the use of halogenated or brominated flame-retardant additives. This is an important distinction from FR-grade ABS or PC, which use chemical additives. Ultem is widely used in aerospace and transit interior applications for this reason.

• Dimensional stability

  Ultem is an amorphous polymer with very low moisture absorption and predictable, consistent dimensional behaviour. This makes it well-suited to precision machined parts where tight tolerances must be maintained in service.

• Stiffness

  Unfilled Ultem is notably stiff for a thermoplastic. Glass-filled grades (typically GF30) are considerably stiffer and stronger, suitable where structural loading is a factor.

• Chemical resistance

  Ultem resists a broad range of chemicals including dilute acids and bases, aliphatic hydrocarbons, and automotive fluids. It is susceptible to attack by partially halogenated solvents and certain chlorinated compounds. Confirm compatibility for your specific chemical environment.

• Machinability

  Ultem machines well on standard CNC equipment. It produces clean surfaces and holds tight tolerances. Unfilled grades machine more smoothly than glass-filled grades; the latter accelerates tool wear.

Typical uses

• Reusable medical instrument trays and sterilisation carriers
• Aerospace interior structural components and ducting
• Semiconductor wafer handling and processing fixtures
• Precision electrical connectors and insulating components
• High-temperature pump and valve components
• Food processing equipment parts requiring thermal resistance

Things to confirm before ordering

• Grade — unfilled (1010, 2010) or glass-filled (1010-GF, 2010-GF30) — glass filling significantly increases stiffness and reduces impact toughness.
• Sterilisation method — Ultem is generally compatible with autoclave steam sterilisation, but confirm the specific grade and cycle conditions with us before ordering for medical use.
• Colour — standard Ultem is an amber/translucent brown; confirm if a specific appearance is required.
• Certifications — if the application requires traceable material certifications, specify this at the time of enquiry.

How does Ultem (PEI) compare?

• PEEK →

  PEEK has a higher maximum continuous use temperature and better chemical resistance (particularly to many solvents that affect Ultem). It is also considerably more expensive. Use Ultem where full PEEK performance is not needed.

• Polycarbonate (PC)

  PC is cheaper and has good impact resistance but a much lower service temperature. It cannot match Ultem for high-temperature, flame-resistance, or precision-instrument applications.