Abstract: Hard and medium density board made of lignocellulosic fibers having a central layer with substantially higher concentration of set resin than both the outer layers of said board have as good strength properties as a corresponding board having said higher concentration of said resin throughout the thickness of the board. Said board is produced by introducing a thermosetting resin solution or a high resin content pulp into and evenly across the width of the central layer of the pulp or the wet lap to be pressed and heat treated, the pressing period being shortened as well as the press cycle. Said process can be carried out with an apparatus including a member to be inserted in the pulp slurry flow in the headbox of a board machine or in the flow on the moving continuous wire screen of the board machine comprising an element having nozzles or slits through which a thermosetting resin solution or a high resin content slurry can be brought to flow.