It has been found possible, by means of the bubble pressure test, to follow the sealing due to the swelling of close cotton cloths when increasing amounts of moisture are present in the fabric. The amount of sealing possible depends on the initial closeness of the fabric; a fabric with a small initial equivalent pore radius can seal more completely than one with twice the initial equivalent pore radius, for the amount to which the fibres and yarns can swell is approximately the same in both cases. In this test, bleached close cotton cloths show a decrease in equivalent pore radius with increasing moisture content beyond saturation regain. Water-repellent cloths, however, show no further decrease of pore size when water is present over the amount corresponding approximately to the supposed saturation regain. A measurable decrease in equivalent pore radius was observed from the dry to wet states in tests on a gaberdine, but because this fabric has a larger initial interstice size the measurements are less precise and show less fractional decrease of pore size than the closer fabrics in oxford or matt weave.