Originally porosity was introduced to layered systems by pillaring. This process involves the intercalation of a guest species to create a porous network. However, the interlayer voids would collapse on removal of the guest species, so pillars were introduced to the framework to maintain the lateral spacing.
Pore size could thus be controlled by the size of the pillar. The spacing in materials synthesised in this fashion was however irregular and the size distribution broad.
This picture shows the type of irregular pores introduced by this method.