Abstract: A device for impregnation of webs of porous materials with a liquid impregnating medium under increased pressure comprises a roller rotatable about a horizontal axis, a trough arranged so that the roller is partially inserted in the trough to form a chamber between an inner surface of the trough and an outer surface of the roller, a unit for supplying an impregnating medium into the chamber, and a unit forming an inlet slot for introducing a web to be impregnated into the chamber and an outlet slot for withdrawing the impregnated web from the chamber. The chamber over a path from the inlet slot to the outlet slot narrows and again increases many times.