1 and 20 2 for example may be used each of which engage with a supporting arm 22 1 and 22 2 which are connected in a permanent manner to the forming head 3 in fig1 the actuators 20 1 and 20 2 as well as the support arms 22 1 and 22 2 are depicted by means of a broken line it is thus possible to expand the sealing of the forming zone 6 in the case of greater spacings between the forming outlet 4 and the deposit belt 8 in an advantageous manner by means of additional sealing walls on all sides of the forming zone 6 in order to optimize the forming zone in particular with the entry of the secondary air flow at the entry end another embodiment example of the device according to the invention is shown in fig3 in a top view of the forming zone 6 this embodiment is substantially identical to the embodiment example according to fig1 and fig2 such that in the following only the differences shall be explained and otherwise reference is made to the aforementioned description as such this embodiment is identical in the cross section view to the embodiment example according to fig1 with the embodiment depicted in fig3 the sealing means 12 3 and 12 4 on the longitudinal surfaces of the forming zone 6 are likewise formed by sealing walls 15 1 and 15 2 the sealing walls 15 1 and 15 2 each include adjustable wall ends 29 1 and 29 2 opposite the entry end 10 the wall ends 29 1 and 29 2 can be adjusted in an.