Is there a consensus on scientific definition of porous materials? There are many definitions out there which do not seem accurate enough:
from wikipedia (accessed July 2017): A porous medium or a porous material is a material containing pores (voids).
-problem : Then almost all materials are porous, since there is some sort of void in everything.
from Merriam Webster (website accessed July 2017): Containing pores, permeable to fluids, capable of being penetrated.
-problem : A piece of tubing would be porous since fluid passes through it.
At what scale do we consider the pores to qualify a material as porous? How much does the permeability matter in a formal definition? Is there a convention on defining pores and porous materials that is agreed upon by scientific organizations like IUPAC or ASTM etc?