Pure cellulose grades. Whatman. Thin papers include Grade 3MM Chr, 1 Chr, 2 Chr, 4 Chr, 17 Chr, 20 Chr and 17 Chr. Specifications for each grade are as follows; 3MM Chr: Though widely used as a blotting paper, 3MM Chr is used in both electrophoresis and for general chemistry. A medium thickness paper (0.34 mm) used extensively for general chromatography and electrophoresis. Flow rate is 130 mm/30 min. Grade 1 Chr: Thickness 0.18mm. Flow rate (water) 130mm/30min. The world standard paper for chromatography. One of the thinnest papers, with medium flow rate.