The human clothing environment exists in a constant state of fluctuation, as heat and moisture is continuously exchanged between the body and its surroundings. Thermal insulation and breathability are considered the two most important factors controlling the exchange of heat and moisture while gas permeability and water vapor diffusion are the most important transport properties used to correlate thermal comfort. Laminated fabrics, such as Gore-Tex®, have long been favored by the outdoor industry at large. The pores in Gore-Tex® ePTFE membranes are small enough to block drops of liquid water yet large enough to allow the much smaller water vapor molecules to passively diffuse through. Careful examinations of existing transport property models suggest membranes with smaller fiber diameters, fiber alignment and specially engineered pore structures may offer improved membrane performance. This thesis explores the effect of fiber diameter, fiber alignment, and multilayered constructions on key transport properties. In-plane fiber alignment was found to have no significant effect on air permeability or water vapor diffusion. Multilayered constructions with increasing pore sizes were found to exhibit directional preference or asymmetric transport for both air permeability and water vapor diffusion. Three theories are discussed and future work is proposed.