PEEK, PPSU, and Ultem — picking the right engineering plastic
PEEK (polyether ether ketone) is the premium engineering thermoplastic — used where metal is too heavy, too conductive, or too expensive, and where ordinary plastics fail from heat, chemicals, or sterilization. We machine PEEK, PPSU, and Ultem (PEI) every week for medical device companies, semiconductor tool makers, and aerospace primes.
When to specify PEEK
PEEK is the right answer when your part sees any of: continuous temperature above 180 °C, aggressive chemicals (chlorinated solvents, concentrated acids), repeated steam sterilization, high mechanical load at elevated temperature, or UHV vacuum environments. Typical applications we produce:
- Surgical instrument handles and trial components for implant design validation
- Semiconductor wafer handling fixtures — chemical-resistant and dimensionally stable
- Seal rings and bearings for pumps handling aggressive media
- Aerospace cabin components (flame-retardant PEEK grades meet FAR 25.853)
- High-voltage insulators where PTFE is too soft
Implant-grade sourcing and traceability
For implant trial components or any part that will contact patient tissue for more than 24 hours, you need implant-grade PEEK — either Invibio PEEK-OPTIMA® or Solvay Zeniva®. These are manufactured under master-file submissions to the FDA with full lot traceability and biocompatibility testing per ISO 10993.
We source implant-grade stock on a per-project basis with a signed customer purchase order that names the end application. Certificate of conformance, lot number, and mill cert follow the parts through machining and ship with the final product. See our quality control process for how material certs are tracked.
PPSU — the practical medical plastic
PPSU (Radel R-5500, Udel P-3703) is our recommendation for 70% of medical applications that don't actually need PEEK. It autoclaves to 140 °C indefinitely, survives 1,000+ cycles without embrittlement, has good impact resistance, and costs about a third of PEEK. The trade-off is lower stiffness and an amber color you can't get away from.
Typical PPSU parts we produce: surgical tool handles, autoclavable trays, dental tool housings, catheter hubs, and any autoclavable medical component where the part doesn't see high mechanical load.
Ultem (PEI) — when you need transparency
Ultem 1000 is PEEK's slightly-cheaper, slightly-weaker cousin. Key advantage: Ultem is translucent amber, whereas PEEK is opaque tan. For medical devices where visual inspection of internal features matters (fluid channels, electrical connections), Ultem wins. Continuous service temp is 170 °C, compared to PEEK's 250 °C.
Machining considerations
PEEK and PPSU machine well with carbide tooling, high RPM, and moderate feed. Coolant (water-soluble) helps dimensional stability on long runs. Key gotcha: PEEK's thermal expansion is 6× that of steel, so long prismatic parts (200+ mm) need to equilibrate to room temperature before final inspection — we build this into our process. For tight-tolerance threaded features, we recommend thread inserts rather than cutting threads directly into PEEK.
What this costs
A representative CNC part — say, a 60 × 40 × 20 mm bracket — costs roughly 10× in standard PEEK what it would cost in aluminum 6061. In implant-grade PEEK, closer to 50×. PPSU lands at about 4× aluminum cost. For prototype quantities, we recommend PPSU or Ultem first; step up to PEEK only if testing reveals performance gaps.