Cast Silicone
also RTV
Cast Silicone is a two-part room-temperature-vulcanizing (RTV) silicone rubber (VMQ class) available in platinum-cure and tin-cure chemistries and cast without heat or pressure.
Values for the Shore A 40 condition
Cast Silicone grades and fills
Cast Silicone is supplied in 15 conditions, soft to hard. Shore A 40 is the default FabDigit quotes; the values on this page are for it.
- 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 | |
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 |
Supply forms, finishes and certifications
Ways Cast Silicone is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
FDA-USP-VI | Food / medical grade | Certification |
What is Cast Silicone?
Cast Silicone is a two-part room-temperature-vulcanizing (RTV) silicone rubber (VMQ class) available in platinum-cure and tin-cure chemistries and cast without heat or pressure. It suits hand-poured molds, encapsulation and prototype elastomer parts; the default mix gives 5 MPa tensile strength, 400% elongation and a 1.7 MPa modulus, with Shore A 10 to A 80 durometers plus optical-clear, FDA/USP Class VI, FR V-0, thermally conductive, ESD-conductive and foam options. Tear and abrasion resistance trail polyurethane, and per-part cost is high at volume, so move to LSR injection moulding for production runs. Cast Silicone 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). Cast Silicone has a tensile strength of 5 MPa (0.725 ksi), weaker than 100% of silicone grades. Elongation at break is 400% and the elastic modulus is 0 GPa (2.47×10⁻⁴ Msi).
What is Cast Silicone used for?
- Medical prototypes
- seals
- kitchenware
Advantages
- Ductile — tolerates forming and impact — 400%, better than 100% of silicone grades
- Low, predictable mold shrinkage — 0.2%, better than 100% of silicone grades
Limitations
- Low stiffness — 0 GPa (2.47×10⁻⁴ Msi), worse than 100% of silicone grades
Cast Silicone properties
Typical room-temperature values for Cast Silicone-Shore A 40; bars are the position among silicone grades.
Physical5
Cast Silicone 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 has a tensile strength of 5 MPa (0.725 ksi), weaker than 100% of silicone grades. Elongation at break is 400% and the elastic modulus is 0 GPa (2.47×10⁻⁴ Msi).
Thermal8
Cast Silicone is rated for continuous service to 200°C (392 °F). It conducts heat at 0.2 W/m·K (0.116 BTU/hr·ft·°F), worse than 100% of silicone grades. Thermal expansion is 270 µm/m·K (150 µin/in·°F).
Electrical7
Cast Silicone 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 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's machinability is poor (25/100, better than 50% of silicone grades); formability excellent (92/100).
Common Calculations4
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Working with Cast Silicone
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.
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) |
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.
Equivalent designations
Standards and trade names that resolve to Cast Silicone in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Trade names
- RTV
How much does Cast Silicone cost?
Cast Silicone is a standard-cost silicone ($$), cheaper than about 82% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Cast Silicone — frequently asked
What is Cast Silicone used for?
Cast Silicone is typically used for medical prototypes, seals and kitchenware. In short: platinum-cure silicone; high temp and biocompatible.
What is the tensile strength of Cast Silicone?
Cast Silicone has a typical tensile strength of 5 MPa (0.725 ksi) — weaker than 100% of silicone grades. Strength varies by condition: see the 15 listed tempers.
Is Cast Silicone easy to machine?
Not especially — machinability is rated poor (25/100, better than 50% of silicone grades). Rarely machined; cured parts are best waterjet, laser or die cut, or frozen/backed before knife trimming — flash is removed by tumbling or trimming.
Can Cast Silicone be welded?
Not weldable; join by uncured silicone adhesive, self-bonding tape or platinum-cure over-molding onto a freshly cured, primed surface.
What surface finishes work on Cast Silicone?
Surface replicates the mold finish exactly; pigment in the mix rather than painting — paint only adheres via silicone-compatible primers, and plasma or primer treatment is needed for bonding.
Can Cast Silicone be formed, bent or molded?
Two-part mix by weight, vacuum degas at ~29 inHg, pour in a thin stream to avoid entrapment; RT cure 4–24 h plus optional 1–4 h post-cure at 60–150 °C for full properties and low volatiles.
What is the maximum service temperature of Cast Silicone?
Cast Silicone is rated for continuous use to about 200°C (392 °F), and briefly to 260°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does Cast Silicone cost?
Cast Silicone is a standard-cost silicone ($$), cheaper than about 82% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Can FabDigit make parts in Cast Silicone?
Yes — Cast Silicone 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; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.