Abstract: A method for the continuous manufacture of an undulating or corrugated longitudinal material in which a strip is projected longitudinally in the form of transverse folds between two longitudinal walls defining a passage or corridor having a height exceeding the thickness of the strip, a longitudinal displacement of said walls being caused in the direction of projection of the strip at a speed lower than the linear projection speed and decreasing in the direction of movement, in such a manner as to cause the packing or bunching of the folds inside the passage or corridor along the length of the material.