PEEK vs PI
Polymer · grade comparison
PEEK and PI are both polymer grades, both high performance plastic. PEEK is the stronger of the two: tensile strength 100 MPa (14.5 ksi) against 86 MPa (12.5 ksi) for PI, about 16% more. PEEK is the more ductile: elongation 30% versus 7.5% for PI. PEEK is lighter (1.3 g/cm³ vs 1.43 g/cm³ for PI) and PEEK is stiffer (3.7 GPa vs 3 GPa). On the shop floor, PEEK welds better (fair vs not recommended).
PEEKChoose it when strength drives the design, or when the part is bent, formed or impact-loaded.
PEEK vs PI: propertiesHow to read these bars
- One bar per material. A full bar is the highest value among all polymer grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
How to read these bars
- One bar per material. A full bar is the highest value among all polymer grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
Mechanical
Strength, stiffness, ductility and hardness at room temperature.
Elastic (Young's) Modulus
Shear Modulus
Bulk Modulus
Poisson's Ratio
Tensile Strength (Ultimate)
Yield Strength (0.2% offset)
Elongation at Break
Compressive Modulus
Flexural Strength
Flexural Modulus
Shear Strength
Fracture Toughness (K_IC)
Izod Impact, Notched
Hardness, Shore D
Hardness, Rockwell M
Hardness, Rockwell R
Same in both: Compressive Strength 130 MPa18.9 ksi
Physical
Density and transition temperatures.
Density
Melting Temperature (Tm)
Glass Transition (Tg)
Water Absorption (24 h)
Water Absorption (Saturation)
Refractive Index
Thermal
How each material carries heat and how hot it can run.
Thermal Conductivity
Specific Heat Capacity
Thermal Expansion (CTE, 20–100 °C)
Max Service Temperature (continuous)
Min Service Temperature
Heat Deflection Temp. @ 0.45 MPa
Heat Deflection Temp. @ 1.8 MPa
Vicat Softening Point (B50)
Limiting Oxygen Index
Max Service Temperature (short-term)
Electrical
Conductivity and insulation.
Dielectric Strength
Dielectric Constant (1 MHz)
Dissipation Factor (1 MHz)
Comparative Tracking Index (CTI)
Same in both: Electrical Resistivity 1×10¹⁴ Ω·m3.94×10²¹ µΩ·in · Volume Resistivity 1×10¹⁶ Ω·cm · Surface Resistivity 1×10¹⁵ Ω
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Corrosion Resistance
UV / Weathering Resistance
Manufacturability
FabDigit workshop ratings (0–100 scores) — how each material behaves on the machine.
Machinability
Weldability
Formability (cold)
Polishability
Mold Shrinkage
Melt Flow Rate
Processing Melt Temperature (typ.)
Mold Temperature (typ.)
Sustainability
Primary-production footprint per kilogram.
Embodied Carbon (primary production)
Embodied Water
Same in both: Embodied Energy (primary production) 290 MJ/kg124,678 BTU/lb · Typical Recycled Content 0%
Common Calculations
Ratios derived from the values above.
Specific Strength (UTS / density)
Specific Stiffness (E / density)
Thermal Diffusivity
Same in both: Thermal Shock Resistance Index 0
Strength versus weight
Yield strength against density for every polymer grade in the FabDigit library; the compared grades are highlighted. Up and left is stronger for its weight.
Manufacturing and finishing
| Capability | PEEK | PI |
|---|---|---|
| 3D printing | Yes | — |
| Default condition | Virgin | Unfilled |
| Relative cost | $$$$$ Specialty | $$$$$ Specialty |
| Min. machined wall | 0.8 mm | 0.5 mm |
| Best machined surface | Ra 0.8 µm | Ra 0.8 µm |
| Conductive Coating | Yes | — |
| Dyeing (Nylon) | Yes | — |
| Primer Coating | Yes | — |
| Tinted Coating | Yes | — |
| Vacuum Metallization | Yes | — |
| Waterproof Coating | Yes | — |
Both are offered for CNC machining, Sheet metal and Injection molding. They share 6 finishes: Chrome Plating (Plastic), EMI Shielding Coating, Painting, Soft Touch Coating, Spray Painting, UV Coating.
PEEK vs PI — frequently asked
Is PEEK stronger than PI?
Yes. PEEK has a typical tensile strength of 100 MPa (14.5 ksi) against 86 MPa (12.5 ksi) for PI — about 16% more.
Which is cheaper, PEEK or PI?
Both sit in the same relative cost tier ($$$$$, specialty); the part price will be decided by machining time, tolerance and quantity rather than by the material.
Which is easier to machine, PEEK or PI?
PEEK. Its machinability rates very good (70/100) against good (65/100) for PI; for welding the order is PEEK first (fair, 45/100) then PI (not recommended, 5/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in PEEK and PI side by side — material, machining time, tolerance and finish in one quote. Certified material data ships with the order on request.
Typical handbook values for the conditions named above, normalised for comparison. Hardness on non-Brinell scales is converted approximately for charting only. Request certified data with your order for design-critical properties.