Grade D Coarse porosity, fast flow rate, with a 2.7um size particle retention. Well suited for higher volume and repetitive laboratory filtering. Also ideally used as a general pre-filter to extend primary filter life. Glass microfiber filters are produced from 100% borosilicate glass microfiber without the use of binders or strengthening agents. Depth filtration categorizes filter media that traps particulate within the random matrix of fibers found within the thickness of the media. The efficiency rating of the filter is characteristic of the complex void space structure that develops as the fibers overlap. The fibers used to manufacture these depth filters are smooth and uniform. This permits their characteristically high flow rates while allowing retention of exceptionally small particles and high load capacity.