Silicone Rubber – Casting Rubber for Mould Making

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What is silicone rubber?

Casting rubber is a pourable material that becomes rubber-like once cured. In most cases this means silicone rubber – also known as liquid silicone rubber (LSR) or PDMS (polydimethylsiloxane).

Silicones retain their properties at both low and high temperatures, last longer than natural rubber and are more resistant to chemicals.

At Silicones and More you will find an extensive range of silicone casting rubbers for mould making, divided by chemistry into condensation-cure RTV silicones (tin catalyst) and addition-cure RTV silicones (platinum catalyst).

Main applications of LSR/PDMS

  • →Silicone mould making for polyurethane resin, epoxy resin, polyester, plaster, wax and concrete
  • →Bodycasting & lifecasting (skin contact – choose the appropriate product line)
  • →Sculpture, art reproduction, SFX & prop making
  • →Food moulds (food-safe product lines available)
  • →Electronics potting, optical components & prototyping

Why choose our silicone rubber

  • ✓Professional quality with clear documentation and practical advice
  • ✓Stable performance across a wide temperature range; predictable curing
  • ✓Food-contact-compliant addition lines; skin safe only where the manufacturer explicitly states so
  • ✓Wide hardness range: from very soft gels to hard grades
  • ✓Excellent tear strength and chemical resistance

Addition vs. condensation RTV silicone

Condensation silicone (tin cure)

Simply put: tends to shrink slightly over time (≈1 %/year). Not food-safe; usually more economical and easy to work with.

Good choice: for general moulds without food contact.

  • Cure by releasing by-products (condensate)
  • Release tin compounds
  • Humidity accelerates curing
  • Bond to fresh condensation silicone

Addition silicone (platinum cure)

Simply put: very low shrinkage after curing. Curing can be inhibited by sulphur, amines and nitrogen or metal salts, among others → always run a small test first.

More durable in use; available in food-safe and skin-safe lines.

  • Cure without by-products
  • Virtually no shrinkage
  • Sensitive to contamination (inhibition)
  • Post-curing can improve properties

Chemical resistance & contamination

After curing: addition systems are generally more resistant to chemicals and aggressive resins than condensation systems.

During curing: condensation systems tolerate contamination better; addition systems require clean tools and masters.

Mixing ratios: condensation systems are more forgiving; addition systems require accurate weighing (deviations can prevent curing).

What is PDMS (polydimethylsiloxane)?

PDMS is the base polymer of most silicone rubbers. In cosmetics it is often called dimethicone. In mould making we usually speak of liquid silicone rubber (LSR) or RTV silicone.

Looking for silicone spray for car rubber seals or RTV sealant? Those are separate product lines and categories.

Processing tips (RTV silicone)

  • •Masters clean and sealed; use a compatible release agent
  • •Weigh accurately (especially with addition silicone); mix thoroughly and scrape the sides and bottom of the cup
  • •Degas under vacuum if possible; otherwise pour in a thin, continuous stream from one corner
  • •Build up brush-on moulds in thin layers for an even cure and strength
  • •Keep temperature and relative humidity as specified in the datasheet; allow to cure fully

Product overview

Condensation-cure silicones (RTV, tin catalyst)

Addition-cure silicones (RTV, platinum catalyst)

  • Silicone Addition Gel 840 Clear – potting gel for electronics; pot life ~80 min; cure ~24 h
  • Silicone Addition Clear 0 Super Soft – crystal-clear firm gel; ~50 min / ~3 h
  • SkinClay SFX Silicone – SFX/wounds on skin; pot life 2–4 min; cure 8–10 min
  • Silicone Addition Clear 5 – very soft & clear; ~30 min / ~2 h
  • Silicone Addition Colourless 5 – very soft and stretchy; for masks, props and candle moulds; ~30 min / ~2 h
  • Wacker CENUSIL® M 810 “Pink 10” – soft/flexible; suitable for aggressive resins; ~40 min / ~4 h
  • Wacker ELASTOSIL® Vario 15 (Normal/Fast) – food-contact compliant to BfR XV and FDA 21 CFR 177.2600 (Wacker); Normal ~60 min / ~6 h; Fast ~2 min / ~15 min
  • Silicone Culinair® – food-safe; tested by TÜV Rheinland to § 31 LFGB (passed); ~60 min / ~6 h
  • Silicone Addition Clear 25 – medium hard, glass-clear; ~120 min / ~20 h
  • Silicone Addition Colourless 25 – Shore A 25; very strong (tear strength 30 N/mm, elongation >420 %); shrinkage <0.1 %; for durable moulds and strong end products; ~30 min / ~3–5 h
  • Silicone Addition Yellow 25 – good resistance to epoxy/PU/polyester; ~60 min / ~6 h
  • Wacker ELASTOSIL® M 4601 A/B – medium hard; high short-term temperature resistance; ~90 min / ~12 h
  • Silicone Addition Green 30 – relatively hard; for sturdy moulds; ~60 min / ~6 h
  • Wacker ELASTOSIL® Vario 40 (Normal/Fast) – hard & strong; Normal ~60 min / ~6 h; Fast ~2 min / ~15 min
  • Silicone Addition Colourless 50 – high hardness; shrinkage <0.1 %; self-degassing; ~30 min / ~3 h
  • Plastique Culinair® Fast – kneadable food-contact silicone; ready in ~10 min; pot life ~100 s
  • PlatSil® Gel-OO – ultra-soft (Shore 00-30); certified skin safe by Polytek (FHSA, ASTM D4236, FDA requirements); for lifecasting, SFX prosthetics & theatre masks
  • PlatSil® Gel-10 – soft (Shore A 10); certified skin safe by Polytek (FHSA, ASTM D4236, FDA requirements); highly realistic feel; for lifecasting & SFX prosthetics
  • PlatSil® Gel-25 – Shore A 25; certified skin safe by Polytek (FHSA, ASTM D4236, FDA requirements); high tensile strength (434 psi); for industrial moulds, prototyping & SFX
  • PlatSil® Gel-0020 – ultra-soft (Shore 00-20); certified skin safe by Polytek (FHSA, ASTM D4236, FDA requirements); for prosthetics, SFX & lifecasting
  • PlatSil® Gel-0030 – ultra-soft (Shore 00-30); certified skin safe by Polytek (FHSA, ASTM D4236, FDA requirements); for prosthetics, SFX & lifecasting
  • PlatSil® FS-00 – ultra-soft (Shore 00-52/A 5); fast (demould after 30 min); high elongation (1,300 %); for robotics, soft prototypes & SFX
  • PlatSil® FS-10 – Shore 00-60/A 13; fast (demould after 25 min); low viscosity (4,200 mPa·s); for rapid prototyping & PU casting
  • PlatSil® FS-20 – Shore A 20; ultra-low viscosity (3,000 mPa·s); versatile mid-range grade of the FS series for a wide range of applications with short turnaround times
  • PlatSil® HTS-25 – Shore A 25; extreme elongation (>2,000 %); high tear strength (179 pli); for PU, epoxy & polyester casting
  • PlatSil® HTS-40 – Shore A 40; high tear strength (131 pli); excellent chemical resistance; for PU, epoxy & polyester casting
  • CHT QM 270 – Shore A 62; high tear strength (17.4 N/mm); fast demoulding (8–12 h); dimensionally stable, shrinkage <0.1 %; for architecture & the furniture industry
  • SilSo Lite 21030 – self-foaming silicone foam (platinum cure); for potting EV battery modules, electronics & lightweight encapsulation

Additives & auxiliaries

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Order silicone rubber and mould-making sets. Compare addition and condensation silicones, download datasheets and contact our team for friendly, expert advice.