Ahlstrom 615 is a fast filter grade with a rough surface that is intermediate in properties between Grade 617 and Grade 631. Low ash grade contains more than 95% super refined alpha-cellulose and linter fibers.
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.