 This figure is relevant in composites, in mining (particular with regard to the properties of tailings), and in soil science.In geotechnical engineering, it is considered as one of the state variables of soils and represented by the symbol e.

Note that in geotechnical engineering, the symbol formula_4 usually represents the angle of shearing resistance, a shear strength (soil) parameter.Because of this, the equation is usually rewritten using formula_6 for porosity