Abstract: An apparatus for the treatment of a flexible material of great length in a treatment volume, comprising means for giving the material the form of a helix comprising several turns, means for causing this helix to progress or advance in the treatment volume by being driven by rotating supporting shafts and means for regulating the speed of entry of the material into the volume and also its speed of progression the treatment volume comprising at least two treatment chambers disposed side-by-side, the entry of the material into one chamber being substantially opposite the exit of the material from the following chamber, and means appropriate for guiding the material from one chamber to the following chamber without driving the said material, wherein said means for guiding said material are formed of a tunnel equiped with two trains of idler rollers.