The roughness is an important property of paper and board, as it has a significant influence on the steps in further processing, e.g. when printing or separating sheets.

The determination of the surface roughness according to Bendtsen is carried out according to ISO 8791-2. 10 individual values per side are measured, from which an average value is formed in each case. Thus, 20 samples with dimensions of at least 75 mm x 75 mm are to be cut. This test is suitable for paper, board and cardboard where the roughness is less than 5000 ml/min. The method cannot be used on highly compressible or particularly air-permeable samples.

To determine the roughness according to Bendtsen, air is pressed through a gap between the sample and a metal ring lying on it within a certain time under defined conditions. The measured air volume flow in ml/min represents the result. A lower measured value is an indicator for a smoother surface.