The invention relates to a method and a device for treating a fibre mass, such as for example a nonwoven or a woven. Such fibre masses are conveyed through a pressing mill for treatment where they are pressed in at least one pressing zone by means of a press-roll. By the pressing, a treatment fluid already present in the fibre mass is pressed out of the fibre mass. After the pressing out of the treatment fluid, a second treatment fluid is introduced into the fibre mass. In order to achieve a distribution of the second treatment fluid in the pressed fibre mass as quickly and homogenously as possible, according to the invention it is provided that the treatment fluid is introduced through the pressing surface area into the fibre mass in an expansion region, where the pressing power exerted by the press-roll is reduced in the moving direction of the fibre mass. Here, the pressing surface area is the surface through which the pressing power acts on the fibre mass.