PEEK Properties & Datasheet — Mechanical, Thermal, Electrical
PEEK (polyether ether ketone) properties set it apart from every commodity and engineering thermoplastic: a continuous-use ceiling of 480°F (250°C), tensile strength reaching 14,500 psi unfilled and 29,000 psi in CF30 grade, and chemical resistance that survives most organic solvents, acids, and steam sterilization cycles intact. This datasheet compiles mechanical, thermal, electrical, and chemical resistance values for all stock-shape grades.
At a glance:
- Tensile strength: 14,500 psi (virgin) — 29,000 psi (CF30)
- Flexural modulus: 600,000 psi (virgin) — 1,800,000 psi (CF30)
- Maximum continuous service temperature: 480°F (250°C)
- Glass transition temperature (Tg): 143°C; crystalline melt point (Tm): 343°C
- Density: 1.32 g/cc (virgin); 1.49 g/cc (GF30); 1.42 g/cc (CF30)
- Volume resistivity: >10¹⁶ Ω·cm (virgin)
- Crystallinity: 30–35% in standard extruded stock
Mechanical Properties
PEEK's mechanical profile is unusually temperature-stable. The flexural modulus changes by less than 15% from room temperature up to 100°C in crystalline stock. Above the Tg of 143°C, amorphous regions soften, but the crystalline fraction maintains structural integrity through the continuous-use range.
Tensile and Compressive Data
Impact and Hardness
Filled-Grade Mechanical Comparison
Filled grades sacrifice elongation and impact toughness for stiffness and strength. For parts subject to shock loads or thin cross-sections, virgin PEEK's higher elongation is often the safer choice despite lower modulus.
Thermal Properties
The crystalline structure of properly processed PEEK stock is what delivers its thermal performance. Amorphously quenched PEEK — sometimes produced inadvertently at high injection speeds or with poorly controlled extrusion — has a Tg of only 143°C and essentially no load-bearing capability above that point. Crystalline stock, confirmed by DSC or density measurement, maintains useful stiffness to 240–250°C continuous.
Thermal Data Table
Effect of Fillers on Thermal Properties
GF30 and CF30 grades alter the CTE significantly. Glass fiber reduces CTE in the fiber direction to approximately 1.5 × 10⁻⁵ in/in/°F; carbon fiber drops it further to ~0.8 × 10⁻⁵ in/in/°F in-plane. This anisotropy must be accounted for in tight-tolerance assemblies where filled PEEK rod or sheet is used near dissimilar materials. See the PEEK specifications article for how this interacts with ASTM D6262 dimensional tolerance ranges.
Electrical Properties
Insulation Grades (Virgin PEEK)
Virgin PEEK's combination of high dielectric strength and low dissipation factor makes it suitable for high-frequency electrical insulation components where dimensional stability under thermal cycling is also required.
ELS Grade (Electrostatic)
ELS PEEK is specified when handling semiconductor wafers, sensitive electronics, or explosive environments where charge accumulation is a process or safety risk. It should not be used in applications requiring full electrical isolation.
For ELS PEEK in semiconductor fixture applications, compare with the PEEK applications guide covering wafer handling and etch-bath use cases.
Chemical Resistance
PEEK's chemical resistance derives from its highly regular aromatic backbone and high crystallinity. The table below rates common reagents at room temperature; performance decreases at elevated temperatures.
| Reagent | Resistance | Notes |
|---|---|---|
| Water / steam (autoclave) | Excellent | Negligible absorption; autoclavable at 134°C |
| Aliphatic hydrocarbons | Excellent | Jet fuel, diesel, mineral oil |
| Aromatic hydrocarbons | Good | Toluene, xylene — surface attack possible at boil |
| Alcohols | Excellent | IPA, methanol, ethanol |
| Ketones / esters | Good | Acetone — limited swell at low exposure |
| Dilute acids (pH > 2) | Excellent | HCl, HNO₃ at <30% concentration |
| Concentrated H₂SO₄ (>60%) | Poor | Attacks polymer backbone |
| Strong alkalis (NaOH >30%) | Moderate | Some degradation at boil |
| H₂O₂ (piranha, <130°F) | Excellent | Semiconductor wet-etch standard |
| Hydraulic fluids | Excellent | Skydrol and mineral-based |
For semiconductor wet-etch processes above 80°C involving concentrated H₂SO₄/H₂O₂ piranha mixtures, verify lot-specific chemical resistance before deploying PEEK fixtures. Some high-temperature piranha conditions may cause surface oxidation over extended exposure.
Physical and Other Properties
Fatigue and Long-Term Loading Properties
Static property values — tensile strength, flexural modulus — describe what PEEK does in a short-duration test. Engineers designing for real-world duty cycles also need fatigue and creep data.
Creep and Stress Relaxation
PEEK's creep resistance is exceptional for a thermoplastic. At 23°C and 7,250 psi (50 MPa) applied stress, PEEK exhibits less than 1.5% total creep strain over 1,000 hours. At 150°C and 5,000 psi, creep strain over 1,000 hours is approximately 2–3% for virgin PEEK — far lower than polyamide or polycarbonate at the same conditions. GF30 and CF30 grades reduce creep by 40–60% versus virgin under equivalent conditions due to fiber reinforcement constraining chain mobility.
Stress relaxation (the loss of clamp force in bolted joints over time) follows a similar trend. For fastened PEEK joints at elevated temperature, design with relaxation allowance of 15–25% over the first 1,000 hours at temperature, then use that stabilized value as the sustained clamp force basis.
Fatigue (Cyclic Loading)
PEEK's fatigue endurance limit under fully reversed bending is approximately 6,000–7,000 psi (41–48 MPa) at 10⁷ cycles. This is roughly 40–50% of the static tensile strength — a ratio typical of semicrystalline polymers and significantly better than amorphous competitors under cyclic stress. For applications involving cyclic loading (reciprocating pump components, valve seats under pressure cycling), this endurance limit should bound the design stress before applying any safety factor.
Wear Rate and PV Limit
Unfilled PEEK has a wear factor (K) of approximately 1.3 × 10⁻⁸ in³·min/ft·lb·hr (per ASTM D3702) and a limiting PV of about 4,000 ft·psi/min in dry sliding against steel. These values position unfilled PEEK as a moderate-performance bearing material — usable for light-duty bearing applications but not optimized for tribological duty. PEEK-based composite grades with PTFE, graphite, or carbon additives reduce K by an order of magnitude and raise PV limits to 20,000+ ft·psi/min.
How PEEK Properties Compare to Competing High-Performance Plastics
Understanding where PEEK fits in the performance hierarchy helps engineers select the right material without overspending. See the PEEK vs Ultem comparison for a head-to-head look at temperature, cost, and FDA status.
Compared to PAI (Torlon), PEEK gives up about 20°F of continuous-use rating and some compressive strength, but gains FDA clearance and better chemical resistance against alkalis. Against Delrin, PEEK is dramatically stronger at temperature but costs 10–15× more per pound.
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