Ultem (PEI) vs PSU (Polysulfone)
Ultem (PEI) and PSU (polysulfone) are both amorphous, high-performance plastics prized for strength, heat resistance, and repeated steam sterilization. Ultem leads on mechanical strength (~105 vs ~70 MPa) and service temperature (~170 vs ~160 C) and is inherently flame-retardant. PSU is somewhat easier to machine and lower in cost. Both resist chemicals strongly and suit demanding medical, aerospace, and fluid-handling roles.
The verdict
Choose Ultem/PEI for the highest strength, temperature, and flame resistance in demanding structural and electronic parts. Choose PSU when you need a sterilizable, chemically resistant, transparent-capable amorphous plastic at lower cost and with easier machining, where PEI's extra performance is not required.
Side-by-side data
| Property | Ultem (PEI) | PSU (Polysulfone) |
|---|---|---|
| Category | Engineering Plastic | Engineering Plastic |
| Density (g/cm³) | 1.27 | 1.24 |
| Tensile strength (MPa) | 105 | 70 |
| Yield strength (MPa) | 105 | 70 |
| Elongation (%) | 60 | 60 |
| Hardness | M109 | M69 |
| Max service temp (°C) | 170 | 160 |
| Machinability | ●●●●● | ●●●●● |
| Corrosion resistance | ●●●●● | ●●●●● |
| Relative cost | ●●●●● | ●●●●● |
| Thermal cond. (W/m·K) | 0.22 | 0.26 |
| Typically used for | High-temp, flame-retardant structural parts | Sterilizable medical & fluid handling |
Which should you choose?
Choose Ultem/PEI when…
- Maximum strength is needed — PEI's tensile (~105 MPa) far exceeds PSU (~70 MPa)
- Higher service temperature is required (~170 C vs PSU ~160 C)
- Inherent flame retardance and low smoke are mandatory (aerospace interiors)
- The part is structural and load-bearing at elevated temperature
- Strong chemical resistance (5/5) and dimensional stability are required
- Electrical and thermal performance for demanding electronics matters
Choose PSU/Polysulfone when…
- Cost is a factor — PSU (~3.5) is cheaper than PEI (~4.5)
- Easier machining is valued (PSU 4.0 vs PEI 3.0)
- Repeated steam and autoclave sterilization are needed for medical/fluid parts
- Transparency or amber translucency is useful
- The application is sterilizable medical or fluid handling per its best-fit use
- PEI's extra strength and temperature are not required
Key differences that matter
- Ultem (PEI) has much higher tensile strength (~105 vs ~70 MPa) and a higher service temperature (~170 vs ~160 C)
- Both are amorphous, high-performance plastics that withstand repeated steam sterilization
- PEI is inherently flame-retardant with low smoke — important for aerospace and transit interiors
- PSU is cheaper (~3.5 vs ~4.5) and machines more easily (4.0 vs 3.0)
- Both rate 5/5 for chemical resistance and serve demanding medical and fluid-handling roles
- PEI is the structural high-temperature choice; PSU is the cost-effective sterilizable option
- Both can be injection molded, machined, and (PEI) 3D printed
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Open the Material SelectorGet a Quote →Frequently asked questions
How much stronger is Ultem than PSU?
Substantially. Ultem (PEI) has a tensile strength around 105 MPa versus polysulfone's ~70 MPa — roughly 50% higher. PEI is also stiffer and holds strength to a higher temperature (~170 vs ~160 C). For load-bearing structural parts at elevated temperature, that strength margin makes PEI the stronger engineering choice.
Can both be sterilized repeatedly?
Yes. Both are amorphous high-performance plastics that tolerate repeated steam autoclaving and other sterilization methods, which is why both appear in medical and fluid-handling applications. PSU is specifically noted for sterilizable medical and fluid parts. PEI adds higher strength and flame resistance for more demanding sterilizable components.
Why is PEI used in aircraft interiors?
PEI is inherently flame-retardant with low smoke and low toxicity emission, plus high strength and a ~170 C service temperature. Those traits meet aerospace interior flammability requirements without added flame-retardant fillers. PSU does not match PEI's flame and strength profile, so for transit and aircraft interior structural parts, PEI is preferred.
When is PSU the better pick?
When you need a sterilizable, chemically resistant amorphous plastic but not PEI's peak strength or flame performance. PSU costs less (~3.5 vs ~4.5), machines more easily (4.0 vs 3.0), and offers useful transparency. For sterilizable medical housings and fluid components where PEI would be over-specified, PSU delivers most of the benefit for less.
Property values are typical/nominal figures for early-stage guidance only and vary by temper, grade, supplier and heat treatment. Confirm critical specifications against a certified datasheet or with an mfgiq engineer before production.