BMI vs PBI
Polymer · grade comparison
BMI and PBI are both polymer grades. PBI is the stronger of the two: tensile strength 160 MPa (23.2 ksi) against 72 MPa (10.4 ksi) for BMI, about 122% more. PBI is the more ductile: elongation 3% versus 2% for BMI. PBI is stiffer (5.9 GPa vs 4 GPa) and PBI runs hotter in service (310°C vs 230°C continuous). On the shop floor, BMI sits in a lower cost tier (high, $$$$) than PBI (specialty, $$$$$).
BMIChoose it when cost is the deciding factor.
PBIChoose it when strength drives the design, or when the part is bent, formed or impact-loaded.
BMI vs PBI: 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
Poisson's Ratio
Tensile Strength (Ultimate)
Elongation at Break
Compressive Strength
Compressive Modulus
Flexural Strength
Flexural Modulus
Shear Strength
Fracture Toughness (K_IC)
Izod Impact, Notched
Hardness, Rockwell M
Physical
Density and transition temperatures.
Glass Transition (Tg)
Water Absorption (24 h)
Water Absorption (Saturation)
Same in both: Density 1.3 g/cm³0.05 lb/in³
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
Limiting Oxygen Index
Max Service Temperature (short-term)
Electrical
Conductivity and insulation.
Electrical Resistivity
Dielectric Strength
Dielectric Constant (1 MHz)
Dissipation Factor (1 MHz)
Volume Resistivity
Surface Resistivity
Comparative Tracking Index (CTI)
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.
Weldability
Polishability
Mold Shrinkage
Processing Melt Temperature (typ.)
Mold Temperature (typ.)
Same in both: Machinability 50 / 100 · Formability (cold) 5 / 100
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)
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 | BMI | PBI |
|---|---|---|
| CNC machining | — | Yes |
| Sheet metal | — | Yes |
| Injection molding | — | Yes |
| Default condition | — | Unfilled |
| Relative cost | $$$$ High | $$$$$ Specialty |
| Min. machined wall | — | 0.5 mm |
| Best machined surface | — | Ra 0.8 µm |
| Chrome Plating (Plastic) | — | Yes |
| EMI Shielding Coating | — | Yes |
| Painting | — | Yes |
| Soft Touch Coating | — | Yes |
| Spray Painting | — | Yes |
| UV Coating | — | Yes |
BMI vs PBI — frequently asked
Is PBI stronger than BMI?
Yes. PBI has a typical tensile strength of 160 MPa (23.2 ksi) against 72 MPa (10.4 ksi) for BMI — about 122% more.
Which is cheaper, BMI or PBI?
BMI is the lower-cost material: it sits in the high tier ($$$$) while PBI is specialty ($$$$$). Part price depends far more on geometry, tolerance and quantity than on raw stock — upload a CAD file for a live quote.
Which welds better, BMI or PBI?
PBI. Its weldability rates not recommended (5/100) against not recommended (0/100) for BMI.
Ready to make it?
Upload a CAD file and FabDigit prices the part in BMI and PBI 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.