When designing components for extreme environments—be it aerospace, medical devices, or oil and gas—engineers often find themselves at the pinnacle of polymer selection: choosing between PEEK (Polyether Ether Ketone) and ULTEM™ (Polyetherimide or PEI). Both are considered high-performance plastics, but their differences in mechanical performance, thermal stability, and cost can be critical to a project’s success.
As experts in the supply and machining of these advanced materials, Cylex Plastics offers this detailed guide to help you make the definitive choice.
I. Material Overview: The Contenders
A. PEEK (Polyether Ether Ketone)
PEEK is often regarded as the gold standard of high-performance thermoplastics. It is a semi-crystalline polymer known for its excellent blend of properties:
- Thermal Stability: Exceptional long-term performance at high temperatures.
- Mechanical Strength: High tensile and flexural strength, coupled with superb creep resistance.
- Chemical Resistance: Highly resistant to a wide range of organic and inorganic chemicals.
B. ULTEM™ (PEI / Polyetherimide)
ULTEM is an amorphous thermoplastic resin manufactured by SABIC (formerly GE Plastics). Often referred to by its chemical name, PEI, ULTEM is known for its excellent rigidity and dimensional stability.
- Rigidity: Offers one of the highest strength-to-weight ratios among amorphous polymers.
- Dielectric Properties: Excellent electrical insulation properties, stable across temperature and frequency ranges.
- Cost-Effectiveness: Generally more economical than PEEK.
II. Head-to-Head Comparison: PEEK vs. ULTEM
Here is a breakdown of how PEEK and ULTEM perform across key engineering metrics:
| Property | PEEK (Polyether Ether Ketone) | ULTEM™ (PEI – Polyetherimide) |
|---|---|---|
| Continuous Use Temperature (Max) | Up to 500°F (260°C) | Up to 340°F (170°C) |
| Mechanical Strength | Superior strength, stiffness, and fatigue resistance (Especially Glass/Carbon Filled Grades). | Excellent rigidity and tensile strength (Lower than PEEK, but better than most standard plastics). |
| Chemical Resistance | Excellent (Highly inert; suitable for prolonged chemical exposure). | Good (Resistant to many hydrocarbons, but sensitive to some strong bases and halogenated solvents). |
| Wear Resistance | Excellent, especially filled grades like PEEK-CF30 (often chosen for bearings and gears). | Good, but generally not as durable as PEEK in severe sliding applications. |
| Sterilization (Medical) | Excellent (Handles repeated steam, radiation, and ETO sterilization). | Very Good (Widely used for repeated steam sterilization). |
| Cost | Higher | Lower (More cost-effective for mid-range temperature needs). |
III. Choosing the Right Material for Your Application
Choose PEEK When…
- Extreme Temperatures are Present: Your components will operate continuously at temperatures above 340°F (170°C)..
- High Fatigue Life is Critical: The part is subjected to repeated stress, such as bearings, seals, or pump gears.
- Chemical Inertness is Required: The material must survive exposure to aggressive solvents, steam, or high-purity water over long periods (e.g., semiconductor and chemical processing).
- You Need Filler Enhancement: You require the absolute highest mechanical properties (e.g., using PEEK-CF30 or PEEK-GF30 for maximum strength).
Choose ULTEM (PEI) When…
- Budget is a Key Constraint: You need high-performance properties at a more economical price point.
- Superior Dielectric Properties are Necessary: The part is an insulator or electrical connector requiring stable electrical properties (e.g., aerospace electrical components).
- High Rigidity is Required: You need an amorphous polymer with high stiffness and excellent dimensional stability for parts like manifolds or electronic enclosures.
- You Need Transparency: Unfilled ULTEM 1000 is an amber-transparent material, offering a window into internal processes (unlike opaque PEEK).
- You Use Glass Filled Grades: You are utilizing grades like ULTEM™2300 30% Glass Filled PEI for a balance of strength and cost.
IV. Conclusion: Matching Polymer to Purpose
Both PEEK and ULTEM are phenomenal high-performance polymers, and Cylex Plastics supplies them in various forms, including Unfilled PEEK Sheet & Rod, ULTEM 1000 PEI, and PEEK Tube. The choice ultimately depends on prioritizing your application’s needs:
- For the absolute maximum in thermal and chemical performance, PEEK is the choice.
- For excellent strength, rigidity, and cost-effectiveness in the mid-range high-temperature segment, ULTEM (PEI) is the superior value.
