The invention relates to a procedure and an apparatus in dry formation of a fibre layer, in which procedure fibre-containing air is passed through a forming wire (7) moving via a former (2) or an equivalent distributor unit and further through a suction box (8) or equivalent placed below the forming wire, and which air is circulated back to the upper part of the same or another former. In the solution of the invention, the air circulated through the suction box (8) is passed to the upper part of the former via channels (17) with an adjustable flow rate.