Thermoplastic comparison
PEEK vs PEI (Ultem)
Every value below is a typical room-temperature figure with its source, test method and conditions — the same dataset that drives the calculators.
Which to choose
PEEK is semi-crystalline: higher continuous service temperature, far better chemical and wear resistance, and the usual answer for bearings, seals and implants. PEI (Ultem) is amorphous — cheaper, dimensionally stable, easier to machine and strong on flame-and-smoke ratings — but some solvents attack it that PEEK simply shrugs off.
| Property | PEEK | PEI (Ultem) | Difference |
|---|---|---|---|
| Density | 1.3 g/cm³ | 1.27 g/cm³ | PEEK — 2% higher |
| Young's modulus E | 3.6 GPa | 3.2 GPa | PEEK — 13% higher |
| Tensile strength | 100 MPa | 105 MPa | PEI (Ultem) — 5% higher |
| Glass transition Tg | 143 °C | 217 °C | PEI (Ultem) — 74 °C higher |
Where these numbers come from
- Callister & Rethwisch, Materials Science and Engineering, 10th ed.
- CAMPUS plastics database — typical grade datasheet values (campusplastics.com)
Typical room-temperature values for learning and preliminary design; grades vary widely and a supplier datasheet always overrides a textbook figure. Confirm against the datasheet before design work.