This model# SS-PTFL-S is an Activated Alumina cartridge. This media is manufactured from aluminium hydroxide in a way that produces this highly porous material.
The porous property of this Activated Alumina compound is what makes it perfect as a filter of fluoride, arsenic, and selenium in drinking water.
It is made of aluminium oxide (alumina), the same substance as rubies and sapphire but, without the impurities that allow those gems to form. Fits all standard 10 in. housings. Replace annually!