This International Standard describes two procedures for measuring the permeability of rubber to gases under steady-state conditions. One uses a horizontal measuring device for measurements at constant pressure and the other uses a vertical measuring device for measurements at constant volume or constant pressure. The results obtained by these procedures may be extrapolated to thicknesses of material different from that of the test piece, providing the rubber is homogeneous and isotropic. The procedures apply to solid rubber of hardness not less than 35 IRHD and to gases such as air, nitrogen, oxygen, hydrogen, liquefied petroleum gas (in gaseous form) and coal gas. Errors may be introduced if the gas used appreciably swells the rubber under test.