Premium Soft Addition Mold Rubber for Professional Mold and Prototype Applications

Silicone Addition Yellow 25 is a pourable, addition-curing (platinum) RTV-2 mold rubber that cures at room temperature. Thanks to added silicone oil, this rubber is softer and more free-flowing than our Green 30: the hardness is Shore A 22 and the viscosity 6,000 mPa·s. The components are mixed 1:1 by weight. The pot life is 60 minutes, the mold can be demolded after 6 hours at 20 °C and reaches full strength after 1 day. The yellow rubber has a tensile strength of 3.9 N/mm² and is suitable for molds with undercuts and for casting epoxy, polyurethane and polyester.

Key Benefits

• Hardness Shore A 22 – soft rubber from which models with undercuts are easy to demold.
• Viscosity 6,000 mPa·s – flows easily around fine details and degasses well.
• Tensile strength 3.9 N/mm² – sufficient strength for repeated demolding.
• Mixing ratio 1:1 by weight – easy to weigh and process.
• Pot life 60 minutes – ample time to pour and degas carefully.
• Full strength after 1 day – quickly ready for the first casts.

Typical Applications

• Molds of models with undercuts.
• Molds for casting resins such as epoxy, polyurethane and polyester.
• Soft, flexible molds for fine details.
• Prototypes and decorative pieces.
• Molds for ornaments and jewelry.

Processing Instructions

1. Stir component A and component B separately and thoroughly first.
2. Weigh A and B in a 1:1 ratio by weight. Only use components with the same lot number.
3. Mix slowly and carefully in a figure-8 motion, without whipping in air.
4. Preferably degas the mixture in a vacuum chamber immediately after mixing.
5. Pour within the 60-minute pot life.
6. Allow the mold to cure for at least 6 hours at room temperature. A slight temperature increase speeds up curing; air bubbles then have less time to escape.

If you want to apply the rubber with a spatula instead of pouring it, add Silicone Thixo A (not Thixo C).

Good to Know: Silicone Oil

This mold rubber contains silicone oil. It does not crosslink and can bleed out slightly over time, which may cause a greasy layer on the mold surface and slight shrinkage. Clean cast parts thoroughly before painting or bonding them.

Important Warning: Inhibition of Addition Silicones

This is an addition-curing silicone (platinum cure). Curing can be disrupted by sulfur, nitrogen, amine compounds and metal salts. These substances are found in, among others, latex gloves, some modelling clays, paints and adhesives, condensation silicones, 1-component silicone sealant, natural rubber and certain 3D printing materials. If in doubt, run a small test first or apply a separating layer of polyvinyl alcohol.

Silicones and More, specialist in high-quality mold rubbers and casting materials for professional makers.

Professional Support

Need a firmer mold with higher tear strength and no oil? Take a look at Silicone Addition Green 30. Unsure which mold rubber best suits your application? Contact us at info@siliconesandmore.com, we are happy to help.