Very often outerwear apparel is made of water resistant yet breathable fabrics, and normally these fabrics have multilayer structures of various polymeric materials. The working mechanisms of water vapor transmission through these fabrics are not well understood. The rate at which these breathable fabrics are able to transmit water vapor is most often measured under standard textile testing conditions of 20℃ and 65% relative humidity, but these tests are often little better than useless in predicting a fabric's performance under 'real' conditions. The experiments described in this paper are designed to test breathable fabrics under more realistic conditions. Water is heated to 33℃ in order to simulate a sweating body, and the rate at which the vapor is transmitted through various breathable fabrics is measured. Experiments involve ambient temperatures of 6, 10, 15, and 20℃, with the relative humidity held at a constant 65% throughout.