What is the definition of porous materials?
I have used the following definition in my presentations:

"Porosity is where a material has accessible voids which are permeable to liquids or gases".

Another definition:

"a  solid with pores, i.e. cavities, channels or interstices, which are deeper than they are wide."

IUPAC also defines different types of porosity based on the diameters of the pores:


Micropores: d &lt; 2 nm
Mesopores: 2 &lt; d &lt; 50 nm
Macropores: d > 50 nm 


M. Thommes, K. Kaneko, A. V. Neimark, J. P. Olivier, F. Rodriguez-Reinoso, J. Rouquerol, K. S. W. Sing, Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Report), Pure Appl. Chem. 2015, 87, 1051.