This International Standard specifies a method for the measurement of the permeability to gases of dense, shaped refractory products. NOTE 1:The method specified takes account of the dynamic viscosity of the gas, and therefore the results obtained may not be directly comparable with those obtained by earlier methods which took no account of viscosity. The determination is generally made by the passage of air. Other gases may be used when required, and the viscosities of air and nitrogen are given.