The Aquasana cartridges are made with extruded coconut shell carbon, and the B cartridge (of the countertop) is impregnated with ATS ion-exchange sorbent resin. The A-cartridge is 5 micron absolute, and the B-cartridge is .5 microns absolute, meaning that particles 200 times smaller than a human hair can not pass through the B cartridge (human hair is 100 microns in thickness).