Transient and sustained thermal sensation of cool double-layer textiles under unsteady heat transfer

In this study, a numerical model of human skin–fat–core tissue in contact with a double-layer textile was developed to characterize thermal sensation under unsteady heat transfer. The subcutaneous heat flux at a depth of 0.2 mm was employed as an indicator of thermal sensation. The model was validated against ten textile samples. For single-layer textiles, the predicted heat flux peak ( Q max ) correlated significantly with both subjective evaluations and the thermal effusivity ( b ) of textiles. Besides, two parameters, Q max and sustained coolness duration ( t s ), were defined to evaluate transient and sustained thermal sensation of double-layer textiles throughout the unsteady state. The effects of outer- and inner-layer thermal conductivity, inner-layer thickness and density, as well as ambient temperature on unsteady thermal sensation were systematically analyzed. The results suggested that the transient coolness was primarily governed by the thermal conductivity of the outer layer, whereas sustained coolness was mainly influenced by the thermal conductivity and density of the inner layer. Additionally, ambient temperature played a critical role in thermal sensation, and materials with lower surface thermal effusivity were preferred under low-temperature conditions to alleviate the initial cold feeling.