The Whatman GF/D glass microfiber filter is considerably faster in flow rate and overall filtration speed than Cellulose filter papers of similar particle retention. 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. Retention: 2.7μm. Diameter: 2.1cm. 100/Pack. Whatman #: 1823-021.