Abstract: A method for fiberizing material and for feeding fiberized material to a further process. Fiberization is performed with a pulper, which includes a primary space for processing the material to be fiberized with a knife assembly rotating on a driving shaft. The material to be processed is forced, in order to fiberize the material, by rotary motion of the knife through a screen assembly, into a secondary space, for supplying the fiberized material further through an expulsion opening of the pulper to further processing. The knife assembly includes a primary knife unit for final preparation of a material to be fed into the pulper, and a secondary knife unit for fiberizing the material to be processed by forcing it to pass first through the secondary knife unit, and through a screen assembly, spaced from the knife assembly by a clearance. An apparatus can apply the method.