Silicone Addition Colourless 25 – Platinum Silicone for Strong Moulds & End Products

Premium Platinum Silicone for Professional Moulds and End Products

Silicone Addition Colourless 25 is a 2-component, platinum-cure (addition-cure) casting silicone with Shore A 25 hardness and exceptional mechanical properties. This high-quality silicone combines high tensile and tear strength (7 N/mm² and 30 N/mm) with very high elongation (>420%) and minimal shrinkage (<0.1%), ideal for durable moulds and strong end products. Free-flowing, self-de-airing and easy to colour with silicone pigment. Simple 1:1 mixing ratio.

Key Benefits

• Exceptional mechanical strength: 7 N/mm² tensile strength and 30 N/mm tear strength for durable moulds that can handle hundreds of casts
• Very high elongation: >420% elongation for flexible applications without tearing or permanent deformation
• Shore A 25 hardness: Optimal balance between flexibility and stability for versatile applications
• Platinum-cure technology: Minimal shrinkage (<0.1%), no inhibition on most substrates, long mould life
• Free-flowing and self-de-airing: 3,900 mPa·s viscosity for excellent detail reproduction without vacuum treatment
• Easy to colour: Transparent with a slight yellowish tint, ideal for colouring with silicone pigment for intense colours

Typical Applications

• Strong, durable moulds for concrete, cement and WetCast precast elements
• Props, masks and flexible decorative elements for SFX, film and theatre
• End products and prototypes where high mechanical strength is required
• Pad printing pads and flexible printing applications in the graphics industry
• Podiatry applications and medical models with a balance between softness and firmness
• Jewellery moulds, design objects and industrial applications

Technical Features

Basic specifications:

• Type: 2-component platinum-cure silicone (polyaddition)
• Mixing ratio: A:B = 100:100 (1:1 by weight)
• Pot life: 30 minutes at 20°C
• Demould time: 3–5 hours at 20°C
• Viscosity: 3,900 mPa·s at 20°C
• Hardness: Shore A 23–27
• Tensile strength: 7 ± 2 N/mm²
• Tear strength: 30 ± 2 N/mm
• Elongation: >420%
• Shrinkage: <0.1%
• Density: 1.03 g/cm³ at 20°C
• Colour: Transparent with a slight yellowish tint

Processing instructions:

1. Carefully mix components A and B in a 100:100 ratio (1:1 by weight) by hand or mechanically
2. Stir slowly in a figure-of-eight motion to prevent air entrapment
3. Process the mixture within the 30-minute pot life
4. Wait until fully cured before demoulding (3–5 hours at 20°C)
5. Curing can be accelerated by heat – every 10°C temperature increase roughly halves the time

Customisation options:

• Reduce hardness: Add silicone oil (note: migrates to the surface over time)
• Thicken for spreading: Add Silicone Thixo A or fumed silica
• Colouring: Use silicone pigment for intense colours

Silicones and More supplies high-quality silicones for professional mould making, SFX, industrial applications and strong end products.

Important Warning: Inhibition in Addition-Cure Silicones

Please note: This is an addition-cure silicone (platinum-cure). These silicones can be inhibited by sulphur, nitrogen, amino compounds and metal salts. If you are unsure whether the products you are using (including gloves, spatulas and cups) contain these ingredients, please do a small test first. These substances are found in many latex gloves, some plasticines, paints and adhesives, condensation-cure silicones, 1-component silicone sealants, natural rubbers and 3D printing materials (especially stereolithography). If you still wish to use these, you will need to apply a protective layer of polyvinyl alcohol (PVA).

Professional Support

Our technical specialists advise on material selection, processing techniques, colouring and optimal results for your specific mould or end-product application. Contact us for technical data sheets, processing guidelines or advice on preventing inhibition in addition-cure silicones.