Latent Heat Loss Through Fabrics During an Alternate Simulated Work–Rest Sequence

Abstract

Humans produce different rates of sweating depending on the intensity level of a given activity. The clothing worn during the activity has a significant effect on the latent heat loss that can occur before, during, and after the activity. The water adsorption and spreading properties of a material yield differences in the amount of heat exchange that can occur between the person and the environment. Current test methods evaluate this using a value known as evaporative resistance, which is used to determine the heat exchange potential of a material. However, this value is only taken once the material has reached “steady state” and does not consider the sweating period before steady state is reached, or the drying period after steady state is reached. Therefore, an area under the curve (AUC) value was derived during these periods to compare the heat exchange properties of different materials. A sweating guarded hot plate was used to simulate different sweat rates, and therefore activity levels, to compare materials constructed of cotton, viscose, polyester, and wool. The overall latent heat loss of the hydrophobic wool was much less compared to the other samples with a gentler slope and lower AUC values than the other samples. It was found that the segment of time analyzed has a significant impact on the conclusion drawn about the latent heat loss of a material, p < 0.0001. Sweat rate also has a significant impact on the heat loss value, p < 0.0001, but is perhaps less useful when comparing samples to each other. It was found that comparing the different periods of the test could yield different conclusions when comparing materials for latent heat loss. Several current test methods do not consider phases outside of the steady state period and therefore miss valuable information pertinent to user comfort during these phases, especially in the post-exercise phase.