As a rule, technical ceramic materials have
no open porosity, and are thus gas tight.
For some materials, however, porosity is desirable. This may
be because thermal stresses are more easily managed by porous
materials, or because larger surface areas are required. Porosity
can be deliberately generated through the appropriate selection
of raw materials, the manufacturing process, and in some cases
through the use of additives. This allows closed and open
pores to be created with sizes from a few nm up to a few µm.
Test procedures for determining open porosity are specified
in DIN EN 623-2.