Fillers for Elastomers

A filler (I) for elastomers, especially for use in rubber- elastic products, contains a microgel consisting of crosslinked diene rubber particles modified with hydroxyl (OH) groups on the surface only. Independent claims are also included for (1) a method for the production of (I) in which the microgel is modified with the aid of an OH group-containing emulsifier in the course of crosslinking (2) rubber mixtures containing (I), especially for the production of parts of vehicle tires (3) vulcanized rubber products, especially car tires, parts of which at least are made from such rubber mixtures.