20 Micron Water Filter. The PureT GCB and BVB series are the finest melt-blown polypropylene sediment depth filters with the best filtration efficiency in the industry. The 2-1/2-inch diameter GCB series and the 4-1/2-inch diameter BVB series are both constructed with multi-layers and manufactured by a unique melt-blown process. Beyond the specifications of ordinary sediment depth filters made of only two or three layers, the PureT GCB and BVB series exceed industry standards with a true gradient density four-layer structure from the outer to the inner surface. This patented four-layer design combined with the unique manufacturing process achieves three to eight times the dirt-holding capacity than similarly sized standard sediment cartridges. High quality construction and unmatched performance make the PURET GCB and BVB series excellent choices for all residential, commercial, and industrial applications. Each Filter Sold Separately.