Aerospace seals & bushings
Hydraulic seals, fuel-system bushings, compressor cages. PEEK runs hot and dry where elastomers fail.
High-performance thermoplastic · CAS 31694-16-3
PEEK (PolyEtherEtherKetone)
The premium engineering plastic. Continuous service to 250 °C, excellent chemical resistance, biocompatible, FDA-approved grades available, and machinable on standard CNC equipment. Standard for aerospace seals, medical implants, semiconductor handling, and oil & gas downhole tools.
UTS
100 MPa
Density
1.32 g/cc
Service T
250 °C
Modulus
3.6 GPa
When to use
Pick PEEK when other plastics give up.
PEEK occupies the unusual space between engineering plastics and metals. It outperforms Delrin, Ultem, and Nylon at temperature, chemical resistance, and load-bearing — and brings biocompatibility and chemical inertness that no metal can match. The trade is cost: PEEK stock runs $100–200/lb, with reinforced grades higher.
The unfilled grade (sometimes called PEEK 450G after Victrex’s product number) is the baseline. Glass-filled (GF30) roughly doubles modulus and improves dimensional stability. Carbon-filled (CF30) doubles strength and modulus and adds electrical conductivity, but is harder to machine. Implant-grade PEEK (per ASTM F2026) is purified for medical use.
Strengths
Why people pay for it.
- Continuous service to 250 °CHighest of the engineering thermoplastics. Holds modulus and strength where Nylon would soften and Delrin would melt.
- Chemical resistanceResistant to most acids, bases, hydrocarbons, and solvents — a notable exception is concentrated sulfuric acid, one of the few solvents that attacks PEEK.
- BiocompatibleImplant-grade PEEK passes ISO 10993 cytotoxicity, sensitization, and intracutaneous reactivity. Standard for spinal cages, cranial implants.
- Self-lubricating, low frictionCoefficient of friction ~0.4 against steel. Great for unlubricated dynamic seals and bushings.
- FDA-approved gradesAvailable for food contact, water contact, and pharmaceutical applications.
- Vacuum compatibleLow outgassing — used in semiconductor wafer handlers and space hardware.
Trade-offs
What you give up.
- Cost$100–200/lb stock for unfilled. Reinforced grades $200–400/lb. Stock cost frequently exceeds machining cost.
- Strength vs. metalsUTS 100 MPa is ~1/3 of 6061 aluminum. Use only when temperature or chemical resistance matters.
- Stress-induced crackingSensitive to internal stresses from machining. Anneal stock before tight tolerance work to prevent post-machining drift.
- UV degradationPEEK yellows in sustained UV. Fine indoors; not for outdoor service without UV-resistant additives.
- Heat sensitivity during machiningAbove 280 °C the polymer softens at the cutting edge. Slow speeds + sharp tools + air or light coolant.
Specs
Mechanical, physical & thermal data.
Properties shown for unfilled PEEK (Victrex 450G or equivalent). Reinforced grades follow.
Mechanical
Properties (unfilled)
| Tensile strength at yield | 100 MPa (14.5 ksi) |
|---|---|
| Tensile elongation at yield | 5% |
| Tensile elongation at break | 30 – 50% |
| Tensile modulus | 3.6 GPa |
| Flexural strength | 170 MPa |
| Flexural modulus | 4.0 GPa |
| Compressive strength | 125 MPa |
| Hardness | M105 / R126 (Rockwell) |
| Izod impact (notched) | 55 J/m |
Source: Victrex 450G datasheet. Glass-filled (GF30): UTS 156 MPa, modulus 9 GPa. Carbon-filled (CF30): UTS 220 MPa, modulus 13 GPa.
Thermal
Temperature performance
| Glass transition (Tg) | 143 °C |
|---|---|
| Melting point (Tm) | 343 °C |
| Continuous service | 250 °C (480 °F) |
| HDT (1.8 MPa) | 152 °C |
| HDT with GF30 fill | 315 °C |
| Thermal conductivity | 0.25 W/m·K |
| CTE (below Tg) | 47 µm/m·°C |
| UL94 flammability Self-extinguishing | V-0 |
Highest continuous service temp of any commercially-machined thermoplastic. Glass and carbon fillers extend this further.
Physical & chemical
At room temperature
| Density | 1.32 g/cc (0.0477 lb/in³) |
|---|---|
| Water absorption 24 hr immersion | 0.5% |
| Dielectric strength | 23 kV/mm |
| Volume resistivity | >10¹⁶ Ω·cm |
| Coefficient of friction vs steel, dry | 0.4 |
| FDA / USP VI compatibility Implant-grade per F2026 | Yes |
| Outgassing (TML) ASTM E595 | 0.13% |
Roughly half the density of aluminum, less than 1/6 of steel. Stiffness-to-weight is competitive with aluminum at moderate temperatures.
Grade selection
Pick the right PEEK for the job.
| Grade | UTS | Modulus | Density | Best for |
|---|---|---|---|---|
| Unfilled (450G) | 100 MPa | 3.6 GPa | 1.32 g/cc | General machining, FDA, medical implant base |
| GF30 (30% glass) | 156 MPa | 9 GPa | 1.50 g/cc | Dimensional stability, structural parts, electrical |
| CF30 (30% carbon) | 220 MPa | 13 GPa | 1.40 g/cc | Highest strength, ESD-safe, semiconductor |
| HPV (PTFE/graphite/CF blend) | 85 MPa | 5 GPa | 1.45 g/cc | Bearings, dynamic seals, low-friction wear |
| Implant grade (Optima LT1) | 100 MPa | 3.6 GPa | 1.32 g/cc | Long-term implants — spinal cages, cranial |
Specifications
Common purchase specs.
ASTM D6262
Standard specification for unfilled PEEK
ASTM F2026
Implant-grade PEEK (medical)
ISO 23936-1
Oil & gas — non-metallic (thermoplastic) materials in contact with production media
MIL-P-46184
Plastic molding compound — PEEK
NORSOK M-710
Oil & gas qualified PEEK grades
FDA 21 CFR 177.2415
Food contact compliance
USP Class VI
Pharmaceutical contact biocompatibility
Machining
How we cut it.
PEEK machines on the same equipment as aluminum but with very different parameters. Sharp tools, slow speeds, generous chip clearance, and minimal heat. Heat is the enemy — once the polymer softens at the cutting edge, the chip welds and finish degrades.
Cutting speed
200–400 SFM roughing, 300–600 SFM finishing with carbide on unfilled. Filled grades (especially CF30) cut slower due to abrasive fiber.
Feed rate
Aggressive constant feed. PEEK doesn’t work-harden, but heat builds if the tool dwells.
Tooling
Polished carbide. Diamond-coated (PCD) for filled grades, especially CF30 — fillers eat regular tools.
Coolant strategy
Air blast or light water-soluble. PEEK doesn’t absorb water, but mineral oil can stress-crack the polymer.
Anneal first
For tight-tolerance parts, anneal stock at 200 °C for 4 hr before machining. Reduces residual stress, prevents post-machining warp.
Stress-relief between roughing and finishing
On thin-wall parts, a 200 °C, 1 hr cycle between operations stabilizes geometry.
Chip evacuation
PEEK chips are lightweight and stringy. Plan for chip removal — pile-up causes heat buildup.
No oil
Avoid sulfurized cutting oils. PEEK is generally chemical-resistant but high-EP additives can stress-crack.
Applications
Where PEEK earns its cost.
Medical implants
Spinal cages, cranial reconstruction plates, orthopedic spacers. PEEK has the bone-modulus match titanium can’t deliver.
Semiconductor & energy
Wafer handling, downhole oil & gas tools (HPHT environments), insulators in vacuum. Inert and dimensionally stable at temp.
Compare
Related materials.
Higher load implant
Ti-6Al-4V →
For implants under high load. PEEK better matches bone modulus; Ti carries higher stress.
Cost / weight
Aluminum 6061 →
When chemical resistance and temperature don’t matter — drops cost dramatically.
Higher temperature
Inconel 718 →
When operating temp exceeds 250 °C — the metal alternative.
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