Thermophysiological Comfort of Sportswear Fabrics
Creators: Islam, Md Rashedul
Publisher: name: University of Alberta Library
Year: 2024

<p>The study explored the thermal comfort behavior of sportswear fabrics using different bench-scale equipment to gain an understanding of heat and moisture transfer mechanisms in the skin-cloth-environment system with or without the presence of the microclimate (i.e., the air layer between the human skin and the cloth layer). It used 27 fabrics of different fiber contents that included cotton, lyocell (regenerated cellulose), wool, polyester, Coolmax® (polyester-based), elastomultiester (polyester-based), recycled polyester, nylon, X-static® (nylon-based), and elastane fibers. Twenty-four fabrics had knitted structures, one warp knit (tricot) and the rest weft knits (single jersey, interlock, and jacquard). The other three fabrics had plain woven structures. The fabric thicknesses varied between 0.083 to 2.19 mm. <br>
The dry thermal effusivity of the fabrics was measured using the stacked method (ASTM D7984-21) and a recently developed air-hoop method. It was found that the thermal effusivity measurements conducted by the stacked method using the applied pressure range specified ASTM D7984-21 (10-50 kPa) compressed the fabric, resulting in a material-based thermal effusivity rather the fabric thermal effusivity. On the other hand, a 1 kPa applied pressure allowed ensuring proper contact between the fabric specimen and the sensor with a minimum effect on the fabric’s three-dimensional structure. This 1 kPa pressure also minimized the fabric deformation when conducting the measurement with the air-hoop method, which provides a closer representation of the situation when fabrics are worn as part of a single-layer garment.<br>
The study extended the measurement of thermal effusivity to wet fabrics using the air-hoop method. Two wetting protocols were developed for saturation levels of 75% or below and 100%. The increase in the wet thermal effusivity with the saturation percentage was higher between 75% and 100% saturation compared to below 75% saturation. The wet thermal effusivity of fabrics at 75% and below was linearly correlated with their dry thermal effusivity values, whereas the wet thermal effusivity of fabrics at 100% saturation level demonstrated a positive non-linear relationship with the amount of water present in the fabric specimens at 100% saturation. Furthermore, when a specific amount of water was added to the fabric specimens, thin fabrics provided higher thermal effusivity values than thick fabrics. <br>
    The study performed dry thermal resistance measurements at various thicknesses and two orientations of the microclimate with airflow parallel and perpendicular to the fabric surface to explore the heat transfer mechanism in the skin-cloth-environment system. For both microclimate orientations, the total dry thermal resistance initially increased with the increase in the microclimate thickness due to the heat resistance offered by the stagnant air layer in the microclimate. Above the critical gap, which was associated with the occurrence of heat convection within the microclimate, the total dry thermal resistance decreased and then slightly re-increased for the horizontal orientation. In the vertical orientation, the total dry thermal resistance plateaued above the critical air gap. The occurrence of early convection within the microclimate was evidenced for fabrics with high air permeability with perpendicular airflow. Fabric thickness was found to be a controlling parameter for the total dry thermal resistance in the absence of a microclimate.<br>
The effect of the microclimate thickness on the water vapor transmission rate (WVTR) of sportswear fabrics was investigated using the upright cup method. The WVTR of fabrics initially decreased with the increase in the microclimate thickness due to the resistance of stagnant air to moist air movement within the microclimate. Above the critical air gap, the WVTR slightly increased due to the occurrence of convection within the microclimate. Ultimately, it plateaued at high microclimate thicknesses. The WVTR was correlated with the fabrics’ air permeability.<br>
    The findings of this study bring new knowledge regarding heat and moisture transfer in the skin-cloth-environment system. They will be invaluable for the sportswear clothing industry so that they can better design fabrics and garments to provide superior thermophysiological comfort. The study also provides unique insights in terms of test methods and protocols for characterizing the comfort of fabrics in a meaningful manner. </p>