PEI (Ultem / Polyetherimide)
Polyetherimide (PEI), best known under the Ultem trade name, is an amorphous high-performance thermoplastic with high heat resistance, inherent flame retardancy and excellent dimensional stability for automotive electronics and under-hood parts.
Overview
Polyetherimide (PEI) is an amorphous high-temperature thermoplastic with a glass transition near 217°C for standard Ultem-type grades. It combines stiffness, creep resistance, inherent flame retardancy (often UL94 V-0 without halogen additives) and stable dielectric properties, making it a staple for under-hood connectors, sensor bodies, lighting components and EV electronics housings where PBT or PA6 would soften. PEI processes by injection moulding, extrusion and machining of stock shapes; additive manufacturing filaments extend prototyping use. Relative to PEEK it is typically lower cost but also lower continuous-use temperature and chemical resistance in some aggressive media. Specifying PEI/Ultem as a distinct high-performance polymer helps OEMs and Tier-1s track specialty resin risk separately from commodity engineering plastics.
Automotive Applications
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Properties
Category
Type
High-Performance Polymer
Available Colors
Available Forms
Key Properties
- Glass transition ~217°C (Ultem 1000 class)
- Inherent UL94 V-0 flame performance (many grades)
- Amorphous — excellent dimensional stability
- Good chemical resistance and dielectric strength
- Machinable and injection-mouldable
- Higher cost than PA/PBT engineering plastics
Technical Specifications
Density
~1.27 g/cm³ (unfilled)
Tensile Strength
~85–110 MPa (unfilled); glass-filled grades higher
Temperature Resistance
Continuous use typically ~170–200°C depending on grade; Tg ~217°C
Sustainability
Sustainability Rating
PEI scrap from moulding can be regrind-limited by colour and property retention. End-of-life recycling streams for PEI are niche versus PP/PA. Long part life and halogen-free FR grades improve in-use sustainability profile.