Thermal resistance analysis of cold-protective clothing using numerical modeling: Influence of natural-based nonwoven fabric structure and wind flow conditions

Natural-based nonwovens featuring hollow fibers are promising for cold-protective clothing due to biodegradability and low thermal conductivity. However, their thermal behavior under varying wind intensities and orientations remains insufficiently understood. This study investigates heat-transfer mechanisms using a two-dimensional numerical model based on the porous media approach under local thermal equilibrium. To account for radiation, a radiative thermal conductivity term was integrated into the energy equation. The methodology employs a novel isolation technique: by simulating an impermeable textile zone while maintaining other transport properties, the coupled effects of conduction and radiation were separated from total heat transfer to quantify the convective contribution. The model was validated against experimental data; results show that increasing thickness is inefficient; a 2.18-fold thickness increase improved thermal resistance by only 9.9%. In contrast, reducing air permeability to levels mimicking a thin film yielded a 2.83-fold improvement by suppressing the convection that initially account for 86.2% of total heat transfer at 4 m/s. These findings indicate that controlling permeability is significantly more critical than increasing bulk for enhancing insulation. This work provides a rigorous framework for designing lightweight, high-performance thermal barriers where a balance between thermal protection and water vapor transmission is essential for cold-protective clothing.