Corrugated stock is manufactured by gluing together two sheets of flat paperboard, typically referred to as linerboard, on either side of a wavy-shaped 'corrugation medium'. This wavy-shaped medium is often referred to as 'flute'. The flute is what gives corrugated fiberboard its strength and structure. Flute is available in multiple thickness options, such as B-flute and E-flute, depending on the specific strength and durability requirements.
The wavy-pattern of the flute often tends to be slightly visible on corrugated packaging as a series of parallel lines. The visibility of this pattern can be minimized by using a thicker cardboard instead of linerboard during the corrugation manufacturing process. Please make sure to communicate any such visual or aesthetic requirements to your account manager at the time of getting a price quote for your specific project.