PEEK vs. Ultem (PEI): Selecting the Optimal Polymer for High-Temperature Applications
The Challenge of Extreme Environments
In aerospace, semiconductor, and medical manufacturing, selecting the right thermoplastic for high-temperature and high-load environments is critical. Two polymers dominate this space: Polyetheretherketone (PEEK) and Polyetherimide (PEI, commonly known as Ultem).
This comparison draws on data from ASTM International polymer standards, ISO 1043 thermoplastic classifications, and manufacturer technical datasheets from Victrex and Sabic. Material selection decisions should always reference current MTRs and OEM specifications.
Thermal Performance: A Side-by-Side Analysis
PEEK's continuous service temperature of 260°C outperforms Ultem's 170°C rating by a substantial margin. For sustained exposure above 180°C — oil & gas downhole tools, aerospace engine nacelle bracketry, semiconductor wafer processing — PEEK is the unambiguous choice. However, medical autoclave sterilization (134°C), automotive under-hood (120–150°C), and solder reflow (peak 260°C seconds) all fall within Ultem's operational envelope at 50–70% lower material cost.
Mechanical Properties Under Thermal Load
At room temperature, unfilled PEEK (100 MPa) and Ultem PEI (105 MPa) are nearly identical. The divergence appears above 150°C — PEEK retains ~60% of tensile strength at 200°C, while Ultem loses majority of load-bearing capacity above its Tg of 217°C. Glass-fiber reinforcement narrows this gap (PEEK 30% GF: 160 MPa; Ultem 2300: 140 MPa) but cannot prevent the matrix from softening above Tg.
Recommendations by Application
| Application | Recommended Material | Rationale |
|---|---|---|
| Aerospace structural bracket (200°C+) | PEEK | Thermal load exceeds Ultem capability |
| Medical autoclave tray (134°C) | Ultem PEI | Excellent hydrolytic stability; lower cost |
| Oil & gas downhole connector | PEEK | Chemical exposure + 200°C+ |
| High-density electrical connector | Ultem PEI | Inherent V-0, excellent dielectric |
Both materials are exceptional engineering thermoplastics — match the material to the specific demands rather than defaulting to one or the other.
References & Industry Standards
- ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
- ISO. ISO 1043 — Plastics — Symbols and Abbreviated Terms. iso.org
- National Institute of Standards and Technology (NIST). Polymer Properties Database. nist.gov
- UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
- MatWeb — Material Property Data. matweb.com