Permeance

Permeance, in general, is the degree to which a material admits a flow of matter or energy. Permeance is usually represented by a curly capital P:.

Electromagnetism

In electromagnetism, permeance is the inverse of reluctance. In a magnetic circuit, permeance is a measure of the quantity of magnetic flux for a number of current-turns. A magnetic circuit almost acts as though the flux is conducted, therefore permeance is larger for large cross-sections of a material and smaller for smaller cross section lengths. This concept is analogous to electrical conductance in the electric circuit.
Magnetic permeance is defined as the reciprocal of magnetic reluctance :
which can also be re-written:
using magnetic circuit #Hopkinson's law: the [magnetic analogy to Ohm's law|Hopkinson's law] and the definition of magnetomotive force :
where:

, magnetic flux,
, current, in amperes,
, winding number of, or count of turns in the electric coil.

Alternatively in terms of magnetic permeability :
where:

, permeability of material,
, cross-sectional area,
ℓ, magnetic path length.

The SI unit of magnetic permeance is the henry, equivalently, webers per ampere.

Materials science

In materials science, permeance is the degree to which a material transmits another substance.

Electromagnetism

Material science

Bombaru, D., Jutras, R., and Patenaude, A., "Air Permeance of Building Materials". Summary report prepared by, AIR-INS Inc. for Canada Mortgage and Housing Corporation, Ottawa, 1988.