COC vs PEI
Polymer · grade comparison
COC and PEI are both polymer grades. PEI is the stronger of the two: yield strength 105 MPa (15.2 ksi) against 60 MPa (8.7 ksi) for COC, about 75% more; tensile strength follows at 105 MPa (15.2 ksi) vs 63 MPa (9.14 ksi). PEI is the more ductile: elongation 60% versus 5% for COC. COC is lighter (1.02 g/cm³ vs 1.27 g/cm³ for PEI) and PEI runs hotter in service (170°C vs 110°C continuous). On the shop floor, PEI welds better (good vs fair) and COC sits in a lower cost tier (high, $$$$) than PEI (specialty, $$$$$).
COCChoose it when weight is the constraint, or when cost is the deciding factor.
PEIChoose it when strength drives the design, or when the part is bent, formed or impact-loaded.
COC vs PEI: 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
Poisson's Ratio
Tensile Strength (Ultimate)
Yield Strength (0.2% offset)
Elongation at Break
Flexural Strength
Flexural Modulus
Izod Impact, Notched
Hardness, Rockwell M
Shear Modulus
Bulk Modulus
Compressive Strength
Compressive Modulus
Shear Strength
Fracture Toughness (K_IC)
Hardness, Shore D
Hardness, Rockwell R
Physical
Density and transition temperatures.
Density
Glass Transition (Tg)
Water Absorption (24 h)
Water Absorption (Saturation)
Refractive Index
Light Transmission
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)
Heat Deflection Temp. @ 0.45 MPa
Heat Deflection Temp. @ 1.8 MPa
Vicat Softening Point (B50)
Limiting Oxygen Index
Max Service Temperature (short-term)
Same in both: Min Service Temperature -50°C-58 °F
Electrical
Conductivity and insulation.
Electrical Resistivity
Dielectric Strength
Dielectric Constant (1 MHz)
Dissipation Factor (1 MHz)
Volume Resistivity
Comparative Tracking Index (CTI)
Same in both: Surface Resistivity 1×10¹⁶ 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
Melt Flow Rate
Processing Melt Temperature (typ.)
Mold Temperature (typ.)
Same in both: Mold Shrinkage 0.6%
Sustainability
Primary-production footprint per kilogram.
Embodied Energy (primary production)
Embodied Carbon (primary production)
Embodied Water
Same in both: Typical Recycled Content 0%
Common Calculations
Ratios derived from the values above.
Specific Strength (UTS / density)
Specific Stiffness (E / density)
Modulus of Resilience
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 | COC | PEI |
|---|---|---|
| CNC machining | — | Yes |
| Sheet metal | — | Yes |
| Injection molding | — | Yes |
| 3D printing | — | Yes |
| Default condition | — | Unfilled (1000) |
| Relative cost | $$$$ High | $$$$$ Specialty |
| Min. machined wall | — | 0.5 mm |
| Best machined surface | — | Ra 0.8 µm |
| Chrome Plating (Plastic) | — | Yes |
| Conductive Coating | — | Yes |
| Dyeing (Nylon) | — | Yes |
| EMI Shielding Coating | — | Yes |
| Painting | — | Yes |
| Primer Coating | — | Yes |
| Soft Touch Coating | — | Yes |
| Spray Painting | — | Yes |
| Tinted Coating | — | Yes |
| UV Coating | — | Yes |
| Vacuum Metallization | — | Yes |
| Waterproof Coating | — | Yes |
COC vs PEI — frequently asked
Is PEI stronger than COC?
Yes. PEI has a typical yield strength of 105 MPa (15.2 ksi) against 60 MPa (8.7 ksi) for COC — about 75% more. Tensile strength is 105 MPa (15.2 ksi) vs 63 MPa (9.14 ksi).
Which is cheaper, COC or PEI?
COC is the lower-cost material: it sits in the high tier ($$$$) while PEI is specialty ($$$$$). Part price depends far more on geometry, tolerance and quantity than on raw stock — upload a CAD file for a live quote.
Which is easier to machine, COC or PEI?
PEI, by a small margin. Both rate good for machinability — 65/100 against 60/100 for COC; for welding the order is PEI first (good, 60/100) then COC (fair, 50/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in COC and PEI 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.