PEI (Ultem) vs PEEK (unfilled): Both high-performance polymers — PEI cheaper but lower performing
PEI (Ultem) vs PEEK (unfilled)
Side-by-side chemical composition and mechanical property comparison.
Overview
PEI (Ultem)
Polyetherimide — high-performance amorphous thermoplastic. Similar properties to PEEK at lower cost but lower impact strength and use temp. Transparent amber color. Tg 217°C, inherent flame resistance (UL94 V-0 at 0.4mm), very low smoke. Hydrolytically stable (2000+ autoclave cycles). Trade name Ultem (SABIC). Used for aerospace interior panels, medical sterilizable devices, electrical insulators, semiconductor handling, and 3D-print build plates.
PEEK (unfilled)
Polyetheretherketone — the premium engineering thermoplastic. Exceptional mechanical properties maintained to 260°C continuous use. Resistant to virtually all organic solvents and acids. Biocompatible (ASTM F2026). Used as metal replacement in aerospace, automotive engine parts, medical implants (spinal cages), semiconductor wafer handling, and oil/gas downhole seals.
| PEI (Ultem) | PEEK (unfilled) | |
|---|---|---|
| Material Number | — | — |
| Category | Polymers | Polymers |
| Standard | ISO 10350 | ISO 10350 |
Mechanical properties
| Property | PEI (Ultem) | PEEK (unfilled) | Unit |
|---|---|---|---|
| tensile_strength | 85–105 | 90–110 | MPa |
| yield_strength | 85–100 | ≥ 90 | MPa |
| elongation | 50–60 | 30–50 | % |
Compatibility Assessment
PEEK has higher UTS (100 vs 90 MPa), higher use temp (260 vs 170°C), semicrystalline (better chemical/fatigue resistance), but costs 3-5x more. PEI is amorphous (transparent), inherently flame-resistant (V-0), and excellent for sterilization. Choose PEI for aerospace interiors/medical where transparency and flame matter; PEEK for structural/chemical.
Frequently Asked Questions
Is PEI (Ultem) the same as PEEK (unfilled)?
PEI (Ultem) and PEEK (unfilled) have a 55% composition overlap. Both high-performance polymers — PEI cheaper but lower performing
Can I replace PEI (Ultem) with PEEK (unfilled)?
Generally not recommended. The compositions differ significantly (55% overlap). These materials have different alloying concepts and are intended for different applications.
What is the difference between PEI (Ultem) and PEEK (unfilled)?
The main differences are in the following elements: overall alloying content. PEI (Ultem) is a Polymers grade, while PEEK (unfilled) is a Polymers grade.
Related Comparisons
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Data provided for reference only. Always verify against the applicable specification for critical applications.
All data is for reference only. Equivalents indicate similarity, not identity. Always verify against the applicable specification for safety-critical applications. materialref.com accepts no liability for decisions based on this data.