A forming box (1) is disclosed to an apparatus for dry forming of a fibrous tissue to e.g. preparation of paper. The forming box (1) is provided with a cloud of airborne fibres via transference pipes (6). Unde r the forming box (1) a forming wire (3) and a vacuum box (5) is placed. In order to achieve a very high capacity as a possibility for the handling of very long fibres, the forming box is prepared without a net or a bottom plate. In place hereof the forming box (1) has an open bottom for release of the fibre material onto the forming wire (3). In the forming box rotating spike rollers (7) are established in such a way that they substantially cover the whole cross sectional area of the forming box. The rotating spike rollers have appeared to make it possible to achieve a very big capacity of formed uniform fibrous tissue on the forming wire and at the time make it possible to handle very long fibres.
