A theoretical model is demonstrated that provides a reliable prediction of thermal transmission through nonwoven structures. The validity of the model is confirmed in experiments that measure the thermal conductivity of various nonwoven barrier fabrics. The model is used to characterize the relative contribution of heat transfer mechanisms to the total heat transmission. It also provides a good explanation of the roles played by fiber and fabric variables in determining the thermal insulation of nonwoven barrier materials.

Using a modified Kawabata Thermolabo apparatus housed in a controlled envi ronmental chamber, we obtained measurements of heat transfer through a specially selected set of jersey knit textile fabrics. We then used analytical models to compute thermal comfort limits based on the experimental values and predetermined estimates of human metabolic activity. The jersey knit fabrics differed primarily on the basis of fiber content: the comparisons were between two knits, both made with 100% polyester fibers of different deniers, and a 100% cotton fabric. This research confirms the results of several previous studies that fabric structural features, not component fibers, are the most important controllers of thermal dissipation in the presence of moisture diffusion. Our results also show that heat transfer is highly related to fabric thickness, bulk density, and air volume fraction. Thermal transfer from a simulated sweating skin surface is strongly correlated with fabric porosity and air permeability.

We report on the perceived comfort data collected while ten female subjects exercised in the hot, humid environment ( 29.4°C, 75% RH) wearing garments made from the three experimental knit fabrics. These findings are related to the fabric thermophys iological comfort data reported in Part I, the mechanical and surface related comfort data in Part II, and the skin alteration data in Part III of this series. At four times during the wear protocol (after acclimation, after 10 minutes of wear, after 40 minutes of exercise, and after 20 minutes of rest following exercise), subjects were asked to indicate overall comfort and thermal, wetness, and contact sensations. There was no difference between the fabrics for wetness or thermal sensation, a result explainable in terms of the extremely small differences in water and heat transport data reported in Part I. The thermal insulation, permeability index, and comfort limit values we calculated predict that differences in perceived thermal and wetness sensation should be minimal. Skin temperature was a significant determinant of perceived thermal comfort in our regression model, but capillary blood flow was not. The regression model for wetness sensation showed that stratum corneum water content and evaporative water loss were statistically significant determinants. Use of wetness-related and contact sensation descriptors differed for the three experimental fabrics. Differences in the wetness-related descriptors appear related to the percent water uptake of the fabrics during exercise. Fiber denier and fabric mechanical and surface feature data were useful in explaining the difference in contact sensations. The fabrics differed in perceived overall comfort. In the regression analysis, capillary blood flow was the only physio logical factor with a statistically significant effect on overall comfort. We suspect a link between the mechanical and surface features and capillary blood flow.

Our analyses using Kawabata instruments confirmed significant differences in phys ical and thermal properties of cotton and polyester single jersey knit fabrics. We at tributed observed differences in fabric physical properties to differences between cotton and polyester fibers and in the fineness of component fibers. We judged comparisons to be useful in forecasting tactile comfort and explaining subjective sensations associated with fabric/skin contact.

We studied stratum corneum water content, water evaporation from the skin surface, capillary blood flow, and skin temperature under three different garments worn by ten female subjects exercising and resting in a hot, humid environment (29.4°C, 75% RH). Single jersey knit fabrics made from 100% 1.5 denier polyester, 100% 3.5 denier polyester, or 100% cotton were made into long sleeve T-shirts and pants. Measures of stratum corneum water content using a microwave probe, evaporative water loss using an Evaporimeter, capillary blood flow using a laser Doppler velocimetry instrument, as well as skin temperature, were assessed on the upper back at four times during the wear protocol. An analysis of variance showed that there were no statistically significant differences in the noninvasive skin measurements under the three fabrics. Statistically significant differences in the skin measurements did occur as the kind of activity differed during the wear protocol. Results are discussed in terms of the fabric thermal and mechanical data presented in Parts I and II of this series.