The Pentek WPX100BB20P Poly String Wound Big Blue Sediment Filter Cartridge is a 20 fibrillated polypropylene wound water filter used for whole house filtration. The advanced string wound design of the Pentek WPX100BB20P allows it to capture sediment dirt rust limescale silt sand and other particulates down to the 100 micron level. The WPX100BB20P is optimal used when the minimization of extractables and/or fiber migration is needed. The Pentek WPX100BB20P will fit all 20 x 4.5 Big Blue/Full Flow water filter housings. This filter is also known by part number 355226-43 / 35522643. It should be replaced when a reduction in water pressure occurs.