Cast Silicone Rubber
Silicone is the elastomer that keeps working when the others have hardened, cracked or melted: it stays flexible from –60 °C to 200 °C (250 °C for special grades), is inert enough for food, skin and implants, does not yellow in sunlight and does not take a set the way urethane does. Cast silicone — a two-part platinum- or tin-cure rubber poured into a printed or machined mold — is how we make prototype and low-volume gaskets, seals, keypads, grips, wearables and soft overmolds before a liquid-silicone-rubber (LSR) injection tool is justified. It is weaker in tear and abrasion than urethane or natural rubber, and nothing bonds to it without a primer, but for temperature, biocompatibility and longevity it has no rival among soft materials.
Silicone by form
Cast silicone (RTV, platinum- or tin-cure)10–70 Shore A · clear, pigmented, food / medical grade1—Prototype and low-volume gaskets, seals, keypads, grips, wearables, soft overmolds and moulds — poured or injected into 3D-printed or machined tooling, cured at room temperature or 60–100 °C. Platinum-cure for clarity, food and medical use; tin-cure for tooling.
Other siliconesLSR, HCR, silicone foam, fluorosilicone2—Liquid silicone rubber for injection-molded production parts; high-consistency rubber for extruded profiles and compression-molded gaskets; closed-cell silicone foam for compliant seals; fluorosilicone where fuel resistance is also needed.
Choose cast silicone for
Seals and gaskets that see heat, steam, ozone or sunlight; keypads, buttons and membrane covers; grips, straps and wearables in contact with skin; medical and food-contact prototypes (USP Class VI and FDA grades); baby, kitchen and lab products; vibration mounts and soft bumpers that must not creep; and moulds themselves — silicone is what we cast urethane parts in. Durometers from 10 to 70 Shore A, clear or pigmented.
Look elsewhere when
The part needs tear or abrasion resistance — tyres, wheels, wear strips, cable jackets (polyurethane or TPU are several times tougher), it must resist fuel, oil or solvents (NBR, FKM), it must be bonded to a hard part without a primer or mechanical lock (nothing sticks to cured silicone), volumes exceed a few hundred (LSR injection molding), or the part must be stiff — silicone is a soft rubber, not a structural material. Tin-cure silicone also inhibits the cure of platinum-cure resins in the same mold.
Loading the library…
Silicone by application
- Seals, gaskets and soft parts
- Choose the durometer for the job: 10–30 A for skin-contact and cushioning, 30–50 A for gaskets and keypads, 50–70 A for grips, feet and bumpers. Medical and food grades on request.
AI suggestions — verify with an engineer before ordering. Estimates are indicative; the quote page prices your exact geometry.
Manufacturing notes
- Tooling
- Moulds are SLA-printed (with a release-coated or post-cured surface so the silicone cures fully), CNC-machined from aluminum or acetal, or — for overmolds — the rigid part itself. Multi-piece moulds with cores handle undercuts; the silicone's flexibility lets us demould geometry a hard part never could.
- Casting
- Two-part silicone is mixed, pigmented, vacuum-degassed and poured or pressure-injected into the mould, then cured at room temperature or in a 60–100 °C oven. Overmolding onto a rigid casting or machined part uses a primer or a mechanical lock. Typical cycle: 1–12 hours per shot depending on the grade; moulds last dozens of shots.
- Tolerance and design
- Expect ±0.2 mm on small features and ±0.5 % overall; wall thickness from 0.5 mm; generous radii. Silicone shrinks little (< 0.5 %) but is compliant, so tolerances on soft parts are usually functional (compression set, sealing force) rather than dimensional.
- Finishing
- Colour in the material (Pantone / RAL match), matte or gloss from the mould surface, translucent or opaque; laser marking and silicone-ink pad printing; slitting, punching and bonding with silicone adhesive. Post-cure bake for medical and food parts to drive off volatiles.
Most-quoted silicone grades
| Grade | Form | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Weldability | Best for |
|---|---|---|---|---|---|---|---|
| Cast Silicone | Cast silicone (RTV, platinum- or tin-cure) | 4 | 5 | 1.1 | Poor | — | Prototype seals, keypads, grips, overmolds |
Finishes for silicone
All 111 finishes3 of our 111 surface finishes take silicone: 2 recommended outright, 1 with process care. Each finish opens to its datasheet — thickness, hardness, salt-spray hours, spec codes and the silicone-specific notes — and the configurator prices it on the grade you pick.
| Finish | Group | On silicone | Thickness, µm | Hardness, HV | Salt spray, h | Cost |
|---|---|---|---|---|---|---|
| Texture Finishing | Mechanical finishing & post-processing | Yes | 0 | — | — | $$$ |
| Trimming | Mechanical finishing & post-processing | Yes | 0 | — | — | $ |
| Degating | Mechanical finishing & post-processing | With care | 0 | — | — | $ |
Silicone — frequently asked
Silicone or polyurethane for a soft part?
Silicone when the part sees heat, cold, sunlight, skin or food, or must keep its shape and softness for years — seals, keypads, wearables, medical and kitchen products. Urethane when the part must be tough — grips that get dragged, wheels, bumpers, cable strain reliefs, anything that will be cut or abraded. Urethane is 3–5 × stronger in tear; silicone survives 200 °C and never yellows.
What durometer should I specify?
Shore A hardness: 10–20 A feels like a gel pad or gummy candy (cushions, skin contact); 30–40 A like a rubber band or keypad; 50–60 A like a pencil eraser or a car tyre tread (grips, gaskets, feet); 70 A like a shoe sole (stiff seals, bumpers). If the part must seal, 30–50 A is the usual range; if it must be gripped or pressed, 40–60 A.
Is cast silicone food-safe or medical-grade?
The platinum-cure grades we use for those parts are — FDA 21 CFR 177.2600 for food contact and USP Class VI / ISO 10993 for skin and short-term medical contact — with a post-cure bake to drive off residual volatiles. Tin-cure silicone is not; it is used for tooling and non-contact parts. Long-term implantable silicone is a separate qualification.
Can silicone be bonded or overmolded onto a hard part?
Yes, with preparation. Cured silicone bonds to almost nothing, so overmolding relies on a silicone primer on the hard part, a self-adhesive silicone grade, or a mechanical lock (through-holes, undercuts, a rim the rubber wraps around). Silicone-to-silicone bonds with silicone adhesive or by co-curing. Design the lock in from the start and the joint will outlast the part.
How many parts can you cast, and what does it cost?
Practical range is 1 to a few hundred: the mould is the cost, the material is cheap. A single mould yields dozens of shots and we run several in parallel for pilot quantities. Above roughly 300–500 pieces, or for very thin or high-precision parts, an LSR injection tool becomes cheaper per part — we can bridge with cast parts while it is made.