The quality of a rotor blade is determined by the reliability of its many adhesives bonds. The use of structural adhesives with a high degree of thixotropy is necessary to prevent the sagging of the adhesive on sloping or vertical surfaces during processing. Currently, there are adhesives based on epoxy resins, polyurethanes, vinyl ester/polyester resins, and methacrylates available for this application. The hydrophobic grades AEROSIL® R 202 and AEROSIL® R 208 are very effective thixotropic agents for use in polar epoxy resin, polyurethane and vinyl ester resin-based adhesives. Furthermore, very good storage stability and processability can be achieved with the latter adhesives when AEROSIL® R 202 and AEROSIL® R 208 are used. AEROSIL® 200 and AEROSIL® 300 are the primarily used thixotropic agents for polyester and methacrylate–based adhesives. The use of AEROSIL® R 711 and AEROSIL® R 7200, which have methacrylate functional groups attached to their surface, can improve even further the mechanical properties and the age resistance of radical curing adhesives or gelcoats.