This forming device is intended to be mounted on a flight (6) of a conveyor for transporting a fibrous product through a heating device, where the flight (6) defines a receiving surface (63) for the fibrous product. The forming device has a forming block (8), a main part (81) of which is intended to be arranged at the front of the receiving surface (63), and at least one anchoring element (9) which is intended to be fixed to the flight by being arranged at the rear of the receiving surface (63). The forming block (8) and the anchoring element (9) comprise complementary snap-fastening members (89, 99) which, when the main part (81) of the forming block (8) is opposite the receiving surface (63) and the anchoring element (9) is fixed to the flight (6) at the rear of the receiving surface (63), are able to engage by the application of a one-way pushing force (F1) that pushes the main part (81) of the forming block (8) towards the receiving surface (63) in a transverse direction (X) with respect to the receiving surface (63).