Silicone Foam (Sponge Rubber) vs Syntactic Foam (Epoxy)
Polymer · grade comparison
Silicone Foam (Sponge Rubber) and Syntactic Foam (Epoxy) are both polymer grades. Syntactic Foam (Epoxy) is the stronger of the two: tensile strength 12 MPa (1.74 ksi) against 1 MPa (0.174 ksi) for Silicone Foam (Sponge Rubber), about 10 times as much. In exchange, Silicone Foam (Sponge Rubber) is the more ductile: elongation 160% versus 1.5% for Syntactic Foam (Epoxy). Silicone Foam (Sponge Rubber) is lighter (0.32 g/cm³ vs 0.45 g/cm³ for Syntactic Foam (Epoxy)) and Syntactic Foam (Epoxy) is stiffer (2.4 GPa vs 0 GPa). On the shop floor, Silicone Foam (Sponge Rubber) machines more easily (very good vs good).
Silicone Foam (Sponge Rubber)Choose it when the part is bent, formed or impact-loaded, or when weight is the constraint.
Syntactic Foam (Epoxy)Choose it when strength drives the design.
Silicone Foam (Sponge Rubber) vs Syntactic Foam (Epoxy): 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.
Silicone Foam (Sponge Rubber)Syntactic Foam (Epoxy)
Mechanical
Strength, stiffness, ductility and hardness at room temperature.
Elastic (Young's) Modulus
Tensile Strength (Ultimate)
Elongation at Break
Compressive Strength
Hardness, Shore A
Tear Strength
Compression Set (22 h, 70 °C)
Shear Modulus
Bulk Modulus
Compressive Modulus
Flexural Strength
Flexural Modulus
Shear Strength
Fracture Toughness (K_IC)
Izod Impact, Notched
Hardness, Shore D
Hardness, Rockwell M
Same in both: Poisson's Ratio 0.3
Physical
Density and transition temperatures.
Density
Glass Transition (Tg)
Water Absorption (24 h)
Water Absorption (Saturation)
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
Limiting Oxygen Index
Max Service Temperature (short-term)
Heat Deflection Temp. @ 0.45 MPa
Heat Deflection Temp. @ 1.8 MPa
Electrical
Conductivity and insulation.
Electrical Resistivity
Dielectric Strength
Dielectric Constant (1 MHz)
Dissipation Factor (1 MHz)
Volume Resistivity
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
Formability (cold)
Mold Shrinkage
Mold Temperature (typ.)
Weldability
Polishability
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)
Same in both: Thermal Diffusivity 0.2 mm²/s · 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 | Silicone Foam (Sponge Rubber) | Syntactic Foam (Epoxy) |
|---|---|---|
| Default condition | — | — |
| Relative cost | $$$$ High | $$$$ High |
| Min. machined wall | — | — |
| Best machined surface | — | — |
Silicone Foam (Sponge Rubber) vs Syntactic Foam (Epoxy) — frequently asked
Is Syntactic Foam (Epoxy) stronger than Silicone Foam (Sponge Rubber)?
Yes. Syntactic Foam (Epoxy) has a typical tensile strength of 12 MPa (1.74 ksi) against 1 MPa (0.174 ksi) for Silicone Foam (Sponge Rubber) — about 10 times as much.
Which is cheaper, Silicone Foam (Sponge Rubber) or Syntactic Foam (Epoxy)?
Both sit in the same relative cost tier ($$$$, high); the part price will be decided by machining time, tolerance and quantity rather than by the material.
Which is easier to machine, Silicone Foam (Sponge Rubber) or Syntactic Foam (Epoxy)?
Silicone Foam (Sponge Rubber). Its machinability rates very good (80/100) against good (60/100) for Syntactic Foam (Epoxy).
Ready to make it?
Upload a CAD file and FabDigit prices the part in Silicone Foam (Sponge Rubber) and Syntactic Foam (Epoxy) 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.