The sol evolves then towards the formation of an inorganic network containing a liquid phase ( gel).

Formation of a metal oxide involves connecting the metal centers with oxo (M-O-M) or hydroxo
(M-OH-M) bridges, therefore generating metal- oxo or metal- hydroxo polymers in solution.

The drying process serves to remove the liquid phase from the gel thus forming a porous material, then a thermal treatment (firing) may be performed in order to favor further polycondensation and enhance mechanical properties.