MATERIAL GUIDE
PEEK vs PEI
Practical material knowledge for better sourcing decisions — written for industrial buyers, not polymer chemists.
TYPICAL REFERENCE VALUES FOR MATERIAL FAMILIES — EXACT VALUES DEPEND ON GRADE AND MANUFACTURER. GRADES AND SPECIFICATIONS ARE CONFIRMED WITH YOU BEFORE EVERY ORDER.
Two Different High-Performance Polymers
PEEK (polyetheretherketone) and PEI (polyetherimide) are both high-performance thermoplastics used in demanding industrial applications, but they are built differently. PEEK is semi-crystalline; PEI is amorphous. That single structural difference drives most of the practical trade-offs between them — temperature capability, chemical resistance, dimensional behavior and price.
Unfilled PEEK is typically rated for continuous service around 260°C. PEI is typically rated around 170°C. If your application runs hot — sealing elements, pump internals, high-temperature fixtures — PEEK has the clear margin. For applications in the 150–170°C range, PEI usually performs well at a materially lower cost.
EDGE · PEEK
PEEK offers outstanding resistance to a broad range of chemicals and performs well in hot-water and steam environments. PEI has good resistance to many chemicals but is attacked by strong alkalis and some solvents — worth checking against your actual media before committing.
EDGE · PEEK
Both materials withstand repeated steam sterilization, which is why both appear in medical and analytical equipment. PEEK additionally handles higher-temperature sterilization cycles.
BOTH · SUITABLE
PEEK retains stiffness and strength better at elevated temperature and in dynamic wear applications; bearing grades (carbon-fibre or PTFE-lubricated) extend this further. PEI offers very stable dimensions and consistent electrical properties — one reason it dominates connectors and test sockets.
DEPENDS · APPLICATION
PEEK: wear rings, seals, semiconductor handling parts, pump and valve components, downhole equipment, medical instruments. PEI: electrical connectors, IC test sockets and burn-in fixtures, inspection tooling, sterilizable medical devices, aircraft interior parts.
TWO DIFFERENT ROLES
Side-by-Side Comparison
| Property | PEEK | PEI |
|---|---|---|
| Structure | Semi-crystalline | Amorphous |
| Continuous service temp. (typ.) | ~260°C | ~170°C |
| Chemical resistance | Outstanding | Good (avoid strong alkalis) |
| Steam sterilization | Suitable | Suitable |
| Wear / bearing grades | Available (CF, PTFE) | Limited |
| Relative cost | High | Mid |
Selection Guidance
CHOOSE PEEK WHEN
CHOOSE PEI WHEN
WHEN IN DOUBT, SEND US THE OPERATING CONDITIONS — BOTH ARE STOCKED, AND GRADE-LEVEL RECOMMENDATION IS PART OF THE SERVICE.
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