This grade has finer particle retention than Ahlstrom 601 but with slightly lower filtration speed. Ahlstrom 642 also has higher absorption than Ahlstrom 601. It is used in general laboratory applications to retain particles above 2 µm in size. Ahlstrom 642 is also found in agricultural and environmental laboratories for plant growth trials, soil testing, and air analysis for monitoring specific contaminants and in the filtration of organic and sulfide precipitates

Standard qualitative filter papers are suitable for quadrant folded or gravity flow applications. These grades contain a high level of alpha-cellulose that provides high purity but will weaken when wet. The inherent strength of standard (untreated) grades does not pose a problem when they are used in routine quadrant folded applications. We do not recommend these grades for use in vacuum work or when wet handling is required.