Ultem 2300 vs Vespel SP-21
Polymer · grade comparison
Ultem 2300 and Vespel SP-21 are both polymer grades. Ultem 2300 is the stronger of the two: tensile strength 169 MPa (24.5 ksi) against 65 MPa (9.43 ksi) for Vespel SP-21, about 160% more. In exchange, Vespel SP-21 is the more ductile: elongation 4.5% versus 3% for Ultem 2300. Ultem 2300 is stiffer (9 GPa vs 3.1 GPa) and Vespel SP-21 runs hotter in service (288°C vs 170°C continuous). On the shop floor, Ultem 2300 welds better (fair vs not recommended).
Ultem 2300Choose it when strength drives the design, or when it will be welded.
Vespel SP-21Choose it when the part is bent, formed or impact-loaded, or when the part sees heat.
Ultem 2300 vs Vespel SP-21: 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)
Yield Strength (0.2% offset)
Elongation at Break
Compressive Strength
Compressive Modulus
Flexural Strength
Flexural Modulus
Shear Strength
Fracture Toughness (K_IC)
Izod Impact, Notched
Hardness, Shore D
Hardness, Rockwell M
Physical
Density and transition temperatures.
Glass Transition (Tg)
Water Absorption (Saturation)
Same in both: Density 1.51 g/cm³0.05 lb/in³ · Water Absorption (24 h) 0.22%
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.
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).
UV / Weathering Resistance
Same in both: Corrosion Resistance 85 / 100
Manufacturability
FabDigit workshop ratings (0–100 scores) — how each material behaves on the machine.
Machinability
Weldability
Polishability
Mold Shrinkage
Melt Flow Rate
Processing Melt Temperature (typ.)
Mold Temperature (typ.)
Same in both: Formability (cold) 10 / 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 | Ultem 2300 | Vespel SP-21 |
|---|---|---|
| Default condition | — | — |
| Relative cost | $$$$ High | $$$$ High |
| Min. machined wall | — | — |
| Best machined surface | — | — |
Ultem 2300 vs Vespel SP-21 — frequently asked
Is Ultem 2300 stronger than Vespel SP-21?
Yes. Ultem 2300 has a typical tensile strength of 169 MPa (24.5 ksi) against 65 MPa (9.43 ksi) for Vespel SP-21 — about 160% more.
Which is cheaper, Ultem 2300 or Vespel SP-21?
Both sit in the same relative cost tier ($$$$, high); the part price will be decided by machining time, tolerance and quantity rather than by the material.
Which is easier to machine, Ultem 2300 or Vespel SP-21?
Vespel SP-21, by a small margin. Both rate good for machinability — 60/100 against 55/100 for Ultem 2300; for welding the order is Ultem 2300 first (fair, 45/100) then Vespel SP-21 (not recommended, 5/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in Ultem 2300 and Vespel SP-21 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.