Abstract: A device for opening flocculent fibrous materials, including a housing and a supply connection pipe having an end extending into a lower portion of the housing for introducing into the housing a negative pressure transport air current conveying fiber flocks. A hollow cylinder is provided that has one end connected to the end of the supply connection pipe, an open end opposite to the one end, and a diameter larger than a diameter of the end of the supply connection pipe. The hollow cylinder forms an annular chamber within the housing. The device further includes a discharge connection pipe connectable to the housing for discharging the fibrous material. The housing, supply connection pipe, hollow cylinder and discharge connection pipe collectively define a pneumatic conveying path for the fibrous material. Additionally provided is a drivable opening disc disposed within the housing and positioned at a distance from and parallel to the open end of the hollow cylinder to extend across the open end.