Parker 23R20A Fulflo Honeycomb Filter Cartridge, String Wound, Cotton FDA Grade Medium and Polypropylene Core, 1" ID, 2-7/16" OD, 20" Length, 5 Micron (Pack of 6) Parker Fulflo Honeycomb series string-wound filter cartridge for multi-purpose industrial process applications Core is polypropylene with string-wound cotton medium for performance consistency Effective nominal 90% removal efficiency at micron rating Irregular outer layer helps reduce surface blinding, helping to ensure longer cartridge life and full utilization of entire cartridge Cotton is FDA/CFR Title 21 compliant, and is acceptable for potable and edible liquid contact