Specifies three methods for determining (in a specified method) the volumes of gas diffusing through the wall of a rubber or plastics hose. The methods involve: determining the permeability of the complete hose wall, excluding end-fittings, to the test gas; determining the permeability of the hose inner lining and the reinforcement to the test gas; and determining precisely the permeability of the wall of a hose during a specified period of time to the test gas. The methods only apply to test gases which are insoluble in water.