Water vapour transfer in waterproof breathable fabrics

To assess the effect of wind speed in practice, experiments were conducted under conditions of realistic wind velocities generated in the climatic chamber. The theoretical and experimental results were compared. In the theoretical model of forced convection between the human skin and the external environment the water vapour transfer rate was found to be proportional to V 0.81 . The experimental results obtained when a layer of fabric was included showed that water vapour transfer is proportional to V 0.5 . The rates of water vapour transfer for the fabrics ranked slightly differently from that seen under steady state conditions; microfibre fabrics, cotton ventiles, PTFE‐laminated fabrics, hydrophilic‐laminated fabrics, and poromeric polyurethane‐laminated fabrics. Condensation was reduced under windy conditions.