Water Vapour Transfer in Wet Waterproof Breathable Fabrics

To answer the question of whether condensation occurring on the inner surface of a waterproof breathable fabric or moisture content within such a fabric has the greater effect on water vapour transfer rate experiments were conducted using two different types of waterproof breathable fabrics under isothermal and non-isothermal conditions. It was found from the experimental results that moisture content and condensation have effects on water vapour transfer in both porous polyurethane and hydrophilic laminated fabrics; higher moisture content and larger amounts of condensation increase the water vapour transfer. The water vapour transfer rate of polyurethane laminated fabrics was greater under isothermal conditions whilst the water vapour transfer rate of hydrophilic laminated fabrics was greater under non-isothermal conditions, especially when a fabric contains more moisture in either form. It was also found that the way moisture content and condensation affect the rate of water vapour transfer is different; the effect of moisture content is greater than that of condensation on water vapour transfer under both isothermal and non-isothermal conditions.