Clothing can influence heat stress depending on the design and its ability to act as a barrier. The progressive heat stress protocol permitted the collection of data to empirically estimate the apparent total evaporative resistance (Re,T,a). Five different clothing ensembles were evaluated, which included work clothes, cotton coveralls, and three limited-use protective clothing ensembles including a pthesis-barrier ensemble, (Tyvek® 1424), water-barrier, vapor-permeable ensemble (NexGen® LS 417), and a vapor-barrier ensemble (Tychem QC®). The study design called for three metabolic level's: low, moderate, and high (L, M, & H) and three heat stages: compensable, transitional, uncompensable (C, T, U). The purpose of this study was to determine if Re,T,a values remained constant over a range of metabolic and heat stage levels. Calculated Re,T,a values were compared using a four-way mixed model analysis of variance. Significant differences for Re,T,a were found among ensembles, metabolic levels, heat stress stages, as well as interactions among ensembles and metabolic levels along with ensembles and heat stress stages (p < 0.0001). A Tukey's Honestly Significant Difference multiple comparison test identified where significant differences occurred (p < 0.05). Results show Re,T,a values differ over a range of metabolic levels and stages of heat stress. Additionally, convection is more supportive of evaporative cooling than diffusion.