Basic corrugated cardboard is produced through joining 3 layers of paper on a corrugating machine. The interior undulating layer of paper is the so-called fluting. Corrugation is formed through passing the fluting through corrugating rolls (rolls with longitudinal grooved structure). They form the undulating pattern. The flat layer of paper is attached to the undulating layer from the top and bottom, with starch glue. When the web has dried, corrugated board can be cut into finished sheets.