thermal transport properties of a series of polyester, cotton, and polyester/cotton blend fabrics were determined in an effort to understand physical basis of clothing comfort. the results indicate that both the fabric construction and the constituent fiber properties affect thermal transport. in general, thermal insulation, air permeability, and water vapor transmission rate are dependent mainly on the fabric geometrical parameters, namely, thickness and porosity. conversely, liquid water transport is strongly dependent on the constituent fibers, with cotton generally showing advantages over polyester. geometrical factors do, however, play a major role in this mechanism, and a 50/50 polyester/cotton blend was nearly identical to cotton in liquid water transport behavior. further, the perceived superior comfort performance of cotton seems largely due to packing behavior in the yarn. 19 refs