This fast filtering grade is an intermediate grade between Ahlstrom 617 and Ahlstrom 631. Ahlstrom 615 has a rough surface and is used for filtering aluminum, ferric and magnesium hydroxides. It is also found in general construction filtration work and in the filtration of insoluble iron and ore.

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.