The ceramic center rod is constructed from a porous white glazed ceramic. A plastic ring made from polypropene sits underneath the tank. There may be an o-ring comprised of a silica gel compound that assists seal the ceramic rod to the plastic ring at the base of the cartridge. https://caidenopaku.izrablog.com/27454131/new-step-by-step-map-for-marijuana-edibles-and-heart-health