Abstract: An apparatus for corrugating a flexible web containing heat softenable fibers comprising two pairs of endless drive chains with paddles mounted to each pair of chains to extend radially outward therefrom. The web is introduced onto the paddles at a point where the paddles are fanned out by passage of the paddles about the arcuate end of the endless chains. The web is folded between the paddles as the separation between the paddles is closed when the paddles move from the arcuate to the straight portion of the endless chains. Heating means soften and bond fibers of adjacent folds of the web together prior to removal of the corrugated web from the paddles.