Wet bulb globe temperature (WBGT) index is used by many professionals in combination with metabolic rate and clothing adjustments to assess whether a heat stress exposure is sustainable. The progressive heat stress protocol is a systematic method to prescribe a clothing adjustment value (CAV) from human wear trials, and it also provides an estimate of apparent total evaporative resistance (R_e,T,a). It is clear that there is a direct relationship between the two descriptors of clothing thermal effects with diminishing increases in CAV at high R_e,T,a. There were data to suggest an interaction of CAV and R_e,T,a with relative humidity at high evaporative resistance. Because human trials are expensive, manikin data can reduce the cost by considering the static total evaporative resistance (R_e,T,s). In fact, as the static evaporative resistance increases, the CAV increases in a similar fashion as R_e,T,a. While the results look promising that R_e,T,s can predict CAV, some validation remains, especially for high evaporative resistance. The data only supports air velocities near 0.5 m/s.