Porosity or
void fraction is a measure of the
void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a
percentage between 0 and 100%. Strictly speaking, some tests measure the "accessible void," the total amount of void space accessible from the surface (cf. closed-cell foam). There are many ways to test porosity in a substance or part, such as
industrial CT scanning. The term porosity is used in multiple fields including
pharmaceutics,
ceramics,
metallurgy,
materials,
manufacturing,
earth sciences,
soil mechanics and
engineering.