An apparatus for producing a longitudinally corrugated product, including: - a guide roll for guiding a web of medium material, - a plurality of flute forming bars (26, 54, 56) oriented generally along a longitudinal axis of the web to define a first corrugating labyrinth effective to longitudinally corrugate, to an intermediate geometry, the web of medium material that is drawn therethrough, said plurality of flute forming bars (26, 54, 56) comprising an upper set of flute forming bars disposed above the web of medium material - a pair of corrugating rollers (28, 30) that cooperate to define, at a nip therebetween, a second corrugating labyrinth between respective and interlocking pluralities of corrugating teeth provided on the corrugating rollers (28, 30), the pluralities of corrugating teeth being arranged cylindrically along each of the rollers (28, 30), wherein said interlocking pluralities of corrugating teeth are effective to longitudinally corrugate, to a substantially final geometry, the web of medium material that is drawn through said nip on rotation of the corrugating rollers (28, 30); and - a web travel pathway for the medium material that follows a path around a portion of an outer circumferential surface of the guide roll, through the first corrugating labyrinth, and through the second corrugating labyrinth; characterized in that - at least a portion of the guide roll is adapted to be arranged at an angle relative to another portion of the guide roll such that a path length of an edge portion of the web is shortened relative to a path length of a center portion of the web after leaving the guide roll; - a lower set of flute forming bars disposed below the web of medium material, said upper and lower sets (50, 52) of flute forming bars (26, 54, 56) being interdigitated so as to define said first corrugating labyrinth; wherein as the web of medium material is actively moving through said first corrugating labyrinth a vertical distance between said upper and lower sets of flute forming bars (50, 52) is adjustable to thereby define a take-up factor for the web of medium material. - a guide roll for guiding a web of medium material, - a plurality of flute forming bars (26, 54, 56) oriented generally along a longitudinal axis of the web to define a first corrugating labyrinth effective to longitudinally corrugate, to an intermediate geometry, the web of medium material that is drawn therethrough, said plurality of flute forming bars (26, 54, 56) comprising an upper set of flute forming bars disposed above the web of medium material - a pair of corrugating rollers (28, 30) that cooperate to define, at a nip therebetween, a second corrugating labyrinth between respective and interlocking pluralities of corrugating teeth provided on the corrugating rollers (28, 30), the pluralities of corrugating teeth being arranged cylindrically along each of the rollers (28, 30), wherein said interlocking pluralities of corrugating teeth are effective to longitudinally corrugate, to a substantially final geometry, the web of medium material that is drawn through said nip on rotation of the corrugating rollers (28, 30); and - a web travel pathway for the medium material that follows a path around a portion of an outer circumferential surface of the guide roll, through the first corrugating labyrinth, and through the second corrugating labyrinth; - at least a portion of the guide roll is adapted to be arranged at an angle relative to another portion of the guide roll such that a path length of an edge portion of the web is shortened relative to a path length of a center portion of the web after leaving the guide roll; - a lower set of flute forming bars disposed below the web of medium material, said upper and lower sets (50, 52) of flute forming bars (26, 54, 56) being interdigitated so as to define said first corrugating labyrinth;