Cast Silicone Shore A 70
Hardness band
also RTV
Shore A 70 = high-hardness cast silicone
Hardest common cast grade: dimensional stability and wear resistance where flexibility is secondary.
Values for the Shore A 70 condition
Other Cast Silicone grades and fills
Cast Silicone is listed in 15 conditions; see the grade overview at Cast Silicone.
- FOAM
- Shore A 10
- TC
- Shore A 20
- ESD-COND
- Sn-cure
- Optical-clear
- Shore A 30
- FR-V0
- Shore A 40
- Pt-cure
- Shore A 50
- Shore A 60
- Shore A 70
- Shore A 80
Compare all 15 grades and fillsHide
| Grade · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness |
|---|---|---|---|---|---|
Silicone foam | Blown low-density cast silicone for thermal/acoustic insulation and compliant compression seals. | — | 1 | 150 | 15 Shore A |
Ultra-soft cast silicone | Gel-like soft grade for skin-like effects, cushioning pads and delicate lifecasting. | — | 2 | 600 | 10 Shore A |
Thermally conductive cast silicone | Alumina/boron-nitride filled potting or gap-pad grade for heat transfer with electrical insulation. | — | 3 | 120 | 55 Shore A |
Soft cast silicone | Soft, highly conformable grade for deep-undercut molds and soft-touch prototypes. | — | 3 | 550 | 20 Shore A |
Electrically conductive / ESD cast silicone | Carbon-black or silver-filled grade for EMI gaskets, contact pads and static-dissipative seals. | — | 4 | 150 | 60 Shore A |
Tin-cure (condensation-cure) cast silicone | Cheaper, inhibition-tolerant mold rubber; higher shrinkage, alcohol by-product and shorter shelf/mold life. | — | 4 | 380 | 35 Shore A |
Optically clear cast silicone | Water-clear unfilled/low-filler formulation for lenses, light guides, encapsulation and display parts. | — | 4 | 350 | 40 Shore A |
Soft mold-making grade | Most common mold-making hardness: easy demolding of detailed or undercut masters. | — | 4 | 450 | 30 Shore A |
Flame-retardant cast silicone | Filled/FR-additive formulation for electrical potting, rail and enclosure seals requiring V-0. | — | 5 | 250 | 50 Shore A |
Shore A 40Default General-purpose cast silicone | Balanced default: enough stiffness for stable mold walls and gaskets, still easily flexed. | — | 5 | 400 | 40 Shore A |
Platinum-cure (addition-cure) cast silicone | Pick for near-zero shrinkage, no cure by-products, long mold life and medical/food compliance; sensitive to sulfur/tin/latex inhibition. | — | 6 | 450 | 40 Shore A |
Medium-hard cast silicone | Choose for seals and pads needing better shape retention and lower deflection under load. | — | 7 | 350 | 11 Shore D |
Hard cast silicone | Stiffer grade for load-bearing gaskets, rollers, bushings and rigid mold shells. | — | 8 | 300 | 16 Shore D |
Shore A 70This page High-hardness cast silicone | Hardest common cast grade: dimensional stability and wear resistance where flexibility is secondary. | — | 9 | 250 | 22 Shore D |
Extra-hard cast silicone | Niche grade for stiff pads, wear strips and rigid inserts; low elongation, higher compression set. | — | 9 | 180 | 30 Shore D |
What is Cast Silicone Shore A 70?
Cast Silicone Shore A 70 is Cast Silicone heat treated to Shore A 70 — hardest common cast grade: dimensional stability and wear resistance where flexibility is secondary. Cast Silicone Shore A 70 has a tensile strength of 9 MPa (1.23 ksi), stronger than 100% of silicone grades. Elongation at break is 250% and the elastic modulus is 0.01 GPa (7.98×10⁻⁴ Msi). Cast Silicone Shore A 70 has a density of 1.1 g/cm³ (0.0397 lb/in³), lighter than 100% of silicone grades. Its glass-transition temperature is -122°C (-188 °F). Shore A 40 is the default condition FabDigit quotes; Shore A 70 is available on request or by drawing note.
Advantages
- Conducts heat well — 0.24 W/m·K (0.139 BTU/hr·ft·°F), better than 150% of silicone grades
Limitations
- Limited ductility — 250%, worse than 100% of silicone grades
- Limited formability — 75/100, worse than 100% of silicone grades
Cast Silicone Shore A 70 properties
Typical room-temperature values for Cast Silicone Shore A 70; 15 are specific to this condition. Other listed values are Cast Silicone reference data and may not represent this condition. Bars are the position among silicone grades.
Physical5
Cast Silicone Shore A 70 has a density of 1.1 g/cm³ (0.0397 lb/in³), lighter than 100% of silicone grades. Its glass-transition temperature is -122°C (-188 °F).
Mechanical7
Cast Silicone Shore A 70 has a tensile strength of 9 MPa (1.23 ksi), stronger than 100% of silicone grades. Elongation at break is 250% and the elastic modulus is 0.01 GPa (7.98×10⁻⁴ Msi).
Thermal8
Cast Silicone Shore A 70 is rated for continuous service to 205°C (401 °F). It conducts heat at 0.24 W/m·K (0.139 BTU/hr·ft·°F), better than 150% of silicone grades. Thermal expansion is 270 µm/m·K (150 µin/in·°F).
Electrical7
Cast Silicone Shore A 70 is an electrical insulator with a dielectric strength of 20 kV/mm (508 V/mil) and a resistivity of 1×10¹³ Ω·m.
Chemical & Environmental3
Corrosion resistance is excellent (85/100), better than 75% of silicone grades. UV resistance is excellent.
Sustainability4
Producing a kilogram of Cast Silicone Shore A 70 takes about 130 MJ of energy and emits 7 kg of CO₂ — less than 100% of silicone grades. Typical recycled content is 0%.
Manufacturability5
Cast Silicone Shore A 70's machinability is poor (33/100, better than 150% of silicone grades); formability very good (75/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Cast Silicone Shore A 70
Is Cast Silicone easy to machine?
Rarely machined; cured parts are best waterjet, laser or die cut, or frozen/backed before knife trimming — flash is removed by tumbling or trimming.
Can Cast Silicone be welded?
Not weldable; join by uncured silicone adhesive, self-bonding tape or platinum-cure over-molding onto a freshly cured, primed surface.
Can Cast Silicone be formed, bent or molded?
Two-part mix by weight, vacuum degas at ~29 inHg, pour in a thin stream to avoid entrapment; RT cure 4–24 h plus optional 1–4 h post-cure at 60–150 °C for full properties and low volatiles.
What surface finishes work on Cast Silicone?
Surface replicates the mold finish exactly; pigment in the mix rather than painting — paint only adheres via silicone-compatible primers, and plasma or primer treatment is needed for bonding.
Cast Silicone chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| silica filler (fumed / ground quartz)reinforcing and extending filler; sets hardness | 15 – 40 | 30 |
| SiH crosslinker (methylhydrogensiloxane)addition-cure systems | 0.5 – 5 | 2 |
| platinum catalyst (Karstedt)Pt-cure only; tin octoate in condensation systems | 5×10⁻⁴ – 0.01 | 0 |
| pigment / inhibitor / additives | 0 – 3 | 1 |
| polydimethylsiloxane (vinyl-terminated Pbase polymer | ≥ 55 (balance) | — |
Cast Silicone Shore A 70 — frequently asked
What is Cast Silicone Shore A 70 used for?
Cast Silicone Shore A 70 is typically used for medical prototypes, seals and kitchenware. In short: platinum-cure silicone; high temp and biocompatible.
What is the tensile strength of Cast Silicone Shore A 70?
Cast Silicone Shore A 70 has a typical tensile strength of 9 MPa (1.23 ksi) — stronger than 100% of silicone grades. Strength varies by condition: see the 15 listed tempers.
Is Cast Silicone Shore A 70 easy to machine?
Not especially — machinability is rated poor (33/100, better than 150% of silicone grades). Rarely machined; cured parts are best waterjet, laser or die cut, or frozen/backed before knife trimming — flash is removed by tumbling or trimming.
Can Cast Silicone Shore A 70 be welded?
Not weldable; join by uncured silicone adhesive, self-bonding tape or platinum-cure over-molding onto a freshly cured, primed surface.
What surface finishes work on Cast Silicone Shore A 70?
Surface replicates the mold finish exactly; pigment in the mix rather than painting — paint only adheres via silicone-compatible primers, and plasma or primer treatment is needed for bonding.
Can Cast Silicone Shore A 70 be formed, bent or molded?
Two-part mix by weight, vacuum degas at ~29 inHg, pour in a thin stream to avoid entrapment; RT cure 4–24 h plus optional 1–4 h post-cure at 60–150 °C for full properties and low volatiles.
What is the maximum service temperature of Cast Silicone Shore A 70?
Cast Silicone Shore A 70 is rated for continuous use to about 205°C (401 °F), and briefly to 260°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Can FabDigit make parts in Cast Silicone Shore A 70?
Yes — Cast Silicone Shore A 70 is available for urethane casting with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM D412 / D624 / D2240 / D395 — rubber tensile, tear, hardness, compression set — ASTM International (2022)
- Engineered Materials Handbook Vol. 2: Engineering Plastics / Elastomers — ASM International (1988)
- Mold Star & Dragon Skin platinum silicone technical bulletins — Smooth-On (2024)
- ELASTOSIL / SILPURAN RTV-2 silicone rubber datasheets — Wacker Chemie AG (2024)
- KE-series RTV silicone rubber product guide — Shin-Etsu Chemical (2023)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.