Device (6) for an installation for forming fibre mats, the fibres being formed from a material that can be drawn by internal centrifuging and by drawing by means of a gas current, the device comprising a guide duct (60) into which the fibres are designed to be channelled, with a longitudinal axis (X) and which has a first portion (61) designed to form the entrance of the duct at which the fibres are designed to be inserted into the said duct, a second portion or central portion (62) and a third portion (63) designed to form the exit of the said duct, characterized in that it comprises articulation means (7) that are suitable for acting mechanically on the third portion of the duct (63) so as to cause its dimension and/or the position of at least one of its portions to vary relative to the said longitudinal axis (X).
