permeance

/ˈpɜːrmiəns/
noun
  1. The ability of a material or substance to allow a fluid or gas to pass through it; the degree to which something is permeable.
    • High permeance in the roofing material helps prevent moisture buildup inside the building.
    • Scientists measured the permeance of the plastic wrap to see if it would keep food fresh.
    • The permeance of the filter determines how much air can flow through it.