PEEK and PEI are both high-performance resins for heat and demanding environments, but they come at the problem differently: PEEK is semi-crystalline, PEI is amorphous.
Side by side
| PEEK | PEI | |
|---|---|---|
| Structure | Semi-crystalline | Amorphous |
| Continuous use temperature | Higher (around 250°C) | High (around 170°C) |
| Chemical resistance | Outstanding | Good; attacked by some solvents |
| Wear and friction | Excellent, especially filled | Good |
| Flame resistance | Inherent | Inherent, low smoke |
| Appearance | Opaque | Transparent amber (unfilled) |
| Dimensional stability | Good | Excellent |
| Relative cost | Very high | High |
Typical, general comparisons. Individual grades vary; check the data sheet.
Choose PEEK when
- The highest heat, harsh chemicals or wear
- Sterilization-heavy medical parts (non-implant)
Choose PEI when
- High heat and strength at a lower cost than PEEK
- Tight tolerances, flame and smoke requirements
- Transparency is useful
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