Whatman wet-strengthened qualitative filter papers have a high wet strength due to the addition of a small quantity of chemically stable resin and are available in both flat and prepleated formats. Prepleated formats, identified by V or 1/2 in the product name, allow improved flow rate and increased loading capacity compared to equivalent flat filters.
Wet-strengthened filter papers are mainly used in normal liquid clarification when filtration is performed under pressure or vacuum and a standard filter is easy to break. Their use in normal qualitative applications will not introduce any significant impurities into the filtrate. The resins do, however, contain nitrogen so these grades should not be used in applications such as Kjeldahl estimations.