Whatman filter papers are categorized into Qualitative and Quantitative filter papers. With the complete range of Whatman qualitative filters, you can be sure the grade that matches a particular application will continue to maintain the performance standards of consistency and quality. The standard grades of qualitative papers are Grade 1: 11um, Grade 2: 8um, Grade3: 6um, Grade 4: 20-25um, Grade 5: 2.5um and Grade 6: 3um. Choose the right filter for the task, with confidence.