A unit for making corrugated board from sheets of paper material comprising: - corrugation means suitable to heat-corrugate sheets of paper material, - the corrugation means comprise a corrugation calender composed of a first and a second corrugation roller and, - heating means suitable to heat sheets of paper material to provide the heat needed to optimize at least the processing performed by the corrugation means, - the heating means comprise a pre-heating station and a heating device, - first gluing means and second gluing means, suitable for joining, by hot gluing, a plurality of sheets of paper material to each other, - the first gluing means and the second gluing means are positioned downstream of the corrugation means and next to it, so that the heating means are suitable to supply 50% to 100% of the heat needed by the first gluing means and the second gluing means, - the first gluing means including first spreading means and a first gluing calender, - the first spreading means being positioned upstream of the first gluing calender and next to it, - the first spreading means being composed of a first spreading calender, - the first gluing calender being positioned downstream of the corrugation calender and of the first spreading calender, and being composed of the second corrugation roller and of a pressure roller, - the second gluing means including second spreading means and a second gluing calender suitable to join the compound corrugated sheet including glue to a final sheet, - the second gluing calender being positioned downstream of the second spreading means, next to it, and being composed of a first and a second pressure roller (20, 21), - the second spreading means being composed of a second spreading calender composed of a second gluing cylinder, - the unit further comprising a plurality of straightening rollers positioned all along the unit and suitable to adjust the trajectory of the sheets of paper and of the compound corrugated sheet, characterized in that the second spreading calender further comprises the first pressure roller. - corrugation means suitable to heat-corrugate sheets of paper material, - the corrugation means comprise a corrugation calender composed of a first and a second corrugation roller and, - heating means suitable to heat sheets of paper material to provide the heat needed to optimize at least the processing performed by the corrugation means, - the heating means comprise a pre-heating station and a heating device, - first gluing means and second gluing means, suitable for joining, by hot gluing, a plurality of sheets of paper material to each other, - the first gluing means and the second gluing means are positioned downstream of the corrugation means and next to it, so that the heating means are suitable to supply 50% to 100% of the heat needed by the first gluing means and the second gluing means, - the first gluing means including first spreading means and a first gluing calender, - the first spreading means being positioned upstream of the first gluing calender and next to it, - the first spreading means being composed of a first spreading calender, - the first gluing calender being positioned downstream of the corrugation calender and of the first spreading calender, and being composed of the second corrugation roller and of a pressure roller, - the second gluing means including second spreading means and a second gluing calender suitable to join the compound corrugated sheet including glue to a final sheet, - the second gluing calender being positioned downstream of the second spreading means, next to it, and being composed of a first and a second pressure roller (20, 21), - the second spreading means being composed of a second spreading calender composed of a second gluing cylinder, - the unit further comprising a plurality of straightening rollers positioned all along the unit and suitable to adjust the trajectory of the sheets of paper and of the compound corrugated sheet,