The invention relates to an apparatus for forming a layered mat of non-oriented particles in a particle board production process, comprising first rollers for size-fractionating a continuous stream of particles into a first and a second fraction; second rollers arranged lower than the first rollers, to receive the first fraction, the second rollers being capable of further size-fractionating said first fraction; and third rollers arranged lower than the second rollers, for receiving said second fraction, the third rollers being capable for further size-fractionating said second fraction; the apparatus further comprising a receiving surface, movable along a longitudinal dimension of the apparatus, and arranged to receive said fractionated first fraction and said fractionated second fraction from said second and third rollers, at different longitudinal positions; wherein the first rollers and the third rollers are pin-type rollers.