Whatman No. GF/D is considerably faster in flow rate and overall filtration speed than cellulose filter papers of similar particle retention (2.7 ¬µm). The filter is thick and consequently exhibits a high loading capacity. Designed as a membrane prefilter and available in sizes to fit most holders. GF/D will provide good protection for finely retentive membranes. Can be used in combination with GF/B to provide very efficient graded prefilter protection for membranes.