Clothing has two primary affects upon workers. First, it modifies the ease with which thermal energy (heat) is transferred between the body and the environment by providing the body with a layer of insulation. This can be advantageous in a thermally dangerous environment (e.g. fire fighting, cold-water immersion), but disadvantageous during strenuous exercise where a significant amount of metabolic heat is produced (Gonzales, 1988). Second, it affects moisture evaporation from the skin surface, and this has a critical impact upon both thermal comfort and body temperature regulation (Candas, 2002). When clothing is worn, evaporation at the skin surface will be reduced, and the extent of this reduction is a function of the properties of the fabric used to manufacture the garment. Thus, less permeable fabrics allow less water vapour to pass through a garment. Some fabrics are designed to allow water vapour, but not water droplets to pass, while others are designed to protect the wearer from chemical, biological and radiological agents, and are almost impermeable. Ensembles made from minimally permeable fabrics are the focus of this project.