A new technique to measure the vapour flow resistance of textiles

The diffusion of water vapour from the human body involves passage through a confined air layer between skin and fabric, through the textile itself, a cid across an outer boundary layer, Measuring the vapour flow resistance of the textile also needs a precise determination of the two air layer resist ances, which is difficult to achieve, These three resistances are first vis ualized on a holographic bench, and then the mass flow is obtained with hig h accuracy using a micro-weighing technique: the evaporation rate is measur ed as a function of time for configurations of one and two fabric layers wh ich seal a calibrated drum of evaporating liquid. Using benzene instead of water gives heavier vapours and a greater and more easily measured evaporat ion rate. The results can be easily converted to their equivalent air thick ness for water vapour, The agreement between theory and measurement leads t o useful insight into the relative importance of the fabric resistance comp ared with that of the two adjoining air layers, The technique described her e is not applicable to all types of textile, especially less porous structu res.