A process for production of silica having variable thickening wherein a) a product stream I containing at least a vaporous, hydrolysable and/or oxidizable silicon compound, b) a product stream II containing oxygen and c) a product stream III containing at least a combustible gas are made to react, where d) a feed port in a pipepiece A, the pipepiece A containing one or more static mixing elements, is used to import product stream I into product stream II, or vice versa and thereby create product stream IV, then e) a feed port in a pipepiece B, the pipepiece B containing one or more static mixing elements, is used to import product stream III in product stream IV and thereby create product stream V, f) product stream V leaving pipepiece B is imported into a reaction chamber, ignited therein and reacted in a flame, and g) the resultant solid material is separated off.