PEI / Ultem Injection Molding: A Buyer's Guide

Specify PEI when you need polycarbonate-like clarity at temperatures PC cannot survive, when aerospace parts must meet flame-smoke-toxicity (FST) rules without additives, or when medical devices need repeated autoclave sterilization. Sold most often as Ultem, it occupies a defined niche in the high-performance tier. See the material selection guide.

PEI Characteristics

PEI (polyetherimide) is an amorphous high-performance thermoplastic. It combines continuous-use temperature resistance with optical transparency (a distinctive amber tint). It is inherently flame retardant with low smoke and toxicity.

As an amorphous resin, PEI has low, uniform shrinkage that helps tight tolerances, an advantage over semi-crystalline peers like PPS and PEEK. Glass-filled grades raise stiffness and strength.

Design and Application Constraints

• High cost. High-performance price tier: well above engineering resins, generally below PEEK.
• Notch sensitivity. Like polycarbonate, sensitive to stress concentrations; radius any sharp internal corners.
• Chemical limitations. Broadly resistant, but attacked by certain chlorinated solvents and strong bases.
• Demanding processing. Very high melt and mold temperatures and strict drying need specialized equipment.

Processing Realities

Verify supplier capability. PEI runs hot enough that molders need oil or electric mold heaters, not standard water cooling.

Drying is strict. Wet PEI degrades structurally during injection. The molder needs dehumidifying dryer protocols. Amorphous shrink often makes tight tolerances easier than with filled semi-crystalline alternatives.

One published datasheet is worth reading with the quote. SABIC’s sheet for unfilled Ultem 1000 lists melt 350–410 °C, mold 135–180 °C, and drying at 150 °C for four to six hours to 0.02% moisture. The buyer-relevant number further down: molding shrinkage of 0.50–0.70%, quoted the same along flow and across it. That symmetry is the amorphous advantage in numbers. It is why a flat PEI part is easier to hold than a flat filled-nylon one, and it is part of what you pay for.

Ranges are grade-specific; confirm against the datasheet for the grade quoted.

Comparing PEI

Against PEEK: PEI is more economical, transparent, and easier to hold dimensionally; PEEK wins on chemical resistance, wear, and ultimate temperature. Against PPS: PEI offers transparency and amorphous stability; PPS broader chemical resistance at lower cost. Against polycarbonate: similar role at a much higher temperature class and price.

Buyer FAQs

What is PEI (Ultem) used for in injection molding?

Aerospace interiors needing inherent FST compliance, reusable medical and dental devices with repeated autoclave cycles, high-temperature electrical insulators, and optical parts in hot environments. If you do not need clarity-at-heat, FST without additives, or autoclave reuse, compare lower-tier options before you pay PEI pricing.

PEI vs PEEK, how do I choose?

PEI when you need transparency, tight dimensional control, inherent FST, or a lower cost inside the high-performance tier. PEEK for aggressive chemicals, severe wear, or the highest continuous operating temperatures. Put that rationale in the RFQ so quotes are comparable.

Is Ultem transparent?

Yes. Unfilled PEI is transparent with a characteristic amber tint. It is not water-clear like acrylic or PC, but it is one of the few polymers with optical transparency at such high temperatures. Glass-filled grades are opaque.

Is PEI hard to injection mold?

It needs specialized high-temperature equipment (hot tooling, high melt) and strict drying. Amorphous shrink makes dimensional behavior more predictable than filled semi-crystalline resins if the molder has the equipment and experience. Do not award without documented oil/electric mold control and drying practice.

Disclaimer

PlasticsTechnologyAlliance.com is an independent buyer resource. It does not manufacture parts, sell materials, or certify suppliers. Material behavior is grade-specific. Confirm properties and suitability against the manufacturer’s datasheet and your supplier’s engineering review.