The wire section of a machine for making a continuous web of fibrous material (esp. a paper-making machine) has two endless sieve belts (2,3) which together form a double sieve zone along part of their length. The surface of at least part of a support element (4) supports the inner face (6) of one sieve belt (2) and the outer surface (7) of the second sieve belt (3) in a support area (I) of the double sieve arrangement. At least one forming box (8) is provided, the location and shape of which in the support area is such that levels of pressure between over-pressure and suction can be adjustably applied in the vicinity of the inner face (9) of the second sieve belt. The forming box extends in the direction of movement of the sieve belts over at least part of the support area (I).
