Unsaturated polyester resins are relatively non polar, as in most cases the reactive diluent styrene is used. For this reason, hydrophilic AEROSIL® fumed silica is the thickening agent of choice. AEROSIL® 200 is widely used for laminating resins and gel coats. Nowadays the more efficient product AEROSIL® 200 HV is recommended.

Some specialty polyester resins and vinyl ester resins, which have more polar character, require hydrophobic AEROSIL® products. AEROSIL® R 202 performs excellent in such formulation, while hydrophilic AEROSIL® fumed silica will not give sufficient thickening efficiency.

The following table shows the typical applications and effects for the use of AEROSIL® and SIPERNAT® products in UP resins and gives recommendations for grades and dosage.