Ceramic bongs, is a form of "pottery" it is made by forming a body of clay, into objects of a perticuliar shape ( in this case bongs ) and heating them to very high temperatures in a kiln ( ceramic oven ) to induce reactions that will change permanently the clay into ceramic. This will increase the ceramic's strength and set their definitive bong shape.
Ceramic bongs are very resistant to heat, unlike metal bongs or pipes, the heat will not transfer has fast. If you ever smoked from a metal pipe , you know what I mean, at some point you cant even hold the bong since it became too hot. Because ceramic has insulating properties and high resistant to heat, this will not happen. Ceramic bongs are also resistant to corrosion, which is a good thing if you put water in your bongs ! Compared to metal bongs, one other advantage that ceramic has is its that it is much lighter, you can easely carry a ceramic bong with you since ceramic bongs tend to be small.