This Pentek 155065-43 RFC-20 Radial-Flow Granular Activated Carbon Filter is constructed with a 70-micron porous polyethylene outer shell and durable polypropylene endcaps. The 2-3⁄4″ outer diameter cartridges have a polypropylene core and the 4-1⁄2″ outer diameter cartridges incorporate a spun polypropylene core. Sandwiched between the outer shell and the core is a bed of granular activated carbon (GAC). The unique radial flow design offers the benefits of granular activated carbon (GAC) filtration, such as low pressure drop, while at the same time significantly reducing the release of carbon fines commonly associated with GAC-style cartridges.