Water vapour permeability is the most important characteristic of any paper, every paper's permeability must be right for its purpose. The paper for packaging cheese requires a very different permeability from the paper permeability of a paper that you don't want to jam up a printer. The vapour permeability required depends entirely on the use of the paper. The Versaperm MK VI water vapour permeability meter is ideal for measuring all paper types.
A Paper's permeability is the measure of how strongly it can resist the passage of a gas - usually water vapour but it could be an other gas such as Oxygen, CO2, Nitrogen or even a hydrocarbon. Vapour permeability dramatically affects the physical characteristics of paper including strength, printability, durability and paper handling(so that it doesn't jam in a machine)
For equipment to measure permeability click here
For an article on measuring the permeability of paper click here