AEROSIL 200 HV Fumed Silica - Thickener for Silicone and Casting Resins

Premium Hydrophilic Fumed Silica Thickener for Professional Silicone and Resin Applications

Fumed Silica Filler (AEROSIL® 200 HV by Evonik) is a hydrophilic, fumed (pyrogenic) silicon dioxide (SiO₂ > 99.8%) used to thicken liquid materials such as silicone, polyester, epoxy and polyurethane and make them thixotropic. The white powder, with a specific surface area of approximately 200 m²/g, dissolves colourless/transparent when mixed well, raises the viscosity to a spreadable or non-sag result and also increases the hardness (Shore value) of silicones. A small amount is enough: for silicones, 1% by weight is often sufficient for a spreadable result.

Key Benefits

• Widely applicable: → thickens silicone, polyester, epoxy and polyurethane.
• Dissolves clear: → white powder that becomes transparent after thorough mixing, without affecting the colour.
• Food-safe in Siliconen Culinair®: → remains food-safe, unlike Thixo A/C.
• Suitable for addition-cure and condensation-cure: → usable in both silicone types, unlike Thixo A/C.
• Increases hardness: → increases the Shore value of silicones as well as the viscosity.
• Unlimited shelf life: → practically unlimited use when stored dry.

Typical Applications

• Thickening silicones (addition-cure and condensation-cure), including food-safe silicones.
• Thixotropic and anti-sag agent in polyester, epoxy and polyurethane resins.
• Paints, coatings, adhesives and sealants as a rheology modifier.
• Reinforcement of HTV and RTV-2 silicone rubber.
• Anti-caking and free-flow agent in powders.

Processing

1. Add the powder gradually to the liquid and mix thoroughly; the viscosity rises during and shortly after mixing.
2. Start low and determine the dosage by trial: start at 0.5% by weight and increase in steps of 0.5%.
3. For silicones, approximately 1% by weight is often sufficient for a spreadable result.

Dosage for polyurethane (by weight of the total resin or of Part A, the polyol):

• 0.7-1%: slightly thickened, non-slump – still easy to pour but stays in place.
• 2-3%: gel-like, ideal for most spatula applications.
• 3-5% (up to 7%): thicker paste (petroleum jelly or peanut butter consistency) for vertical fills or fillets.

Technical Data

• Chemical name: silicon dioxide (fumed), SiO₂
• CAS number: 112945-52-5 / 7631-86-9
• Specific surface area (BET): 175-225 m²/g (nominal 200 m²/g)
• Bulk density: approx. 50 g/l
• pH value (4% dispersion): 3.7-4.5
• SiO₂ content: > 99.8%
• Loss on drying (2 hours at 105°C): ≤ 1.5%
• Colour: white powder (dissolves clear)
• Shelf life: unlimited when stored dry

Special Notes

Although the powder is white, it becomes transparent in the dissolved state after thorough mixing. Unlike Thixo A or Thixo C, Fumed Silica can be used in both condensation-cure and addition-cure silicones, and the result in a food-safe silicone remains food-safe. Fumed Silica also increases the hardness (Shore value) of silicones; Thixo does so to a lesser extent.

Safety

AEROSIL® 200 HV is not classified as hazardous under the CLP Regulation and does not require GHS labelling. Dust may be released when working with the powder; avoid inhaling dust, ensure good ventilation and preferably wear a dust mask and safety goggles. For full information, please refer to the safety data sheet.

This product is AEROSIL® 200 HV from Evonik Operations GmbH, a world leader in the development and production of fumed silica for industrial and technical applications.

Professional Support

Do you have questions about the right dosage for your resin or silicone, or about thickening food-safe silicones? Our specialists will be happy to help. Contact us for personal advice.