Influence of Yarn Micro-Architecture on Coupled Heat and Moisture Transport: Modeling and Validation
Heat and moisture are simultaneously generated during human activity, and evaporative heat loss becomes essential for comfort in warm environments; therefore, transport through voids of textiles must be understood at the structural level. This study uses parallel PET yarns as a controlled system to isolate yarn-scale effects and aims to quantify how packing factor, yarn density, filament number, filament denier, and twist govern moisture resistance under ISO 11092 skin-model conditions. Moisture resistance (Ret), water–vapor permeability (Wd), and heat flux were measured with a sweating guarded hotplate, and a fiber-level two-dimensional representative cross-section of the yarn–air array was built in COMSOL from measured yarn width, thickness, and packing factor, coupling solid heat transfer with diluted water–vapor transport using test-consistent boundary conditions and validated by experimental results. The results show that higher packing factor or higher yarn density reduces the connectivity of inter-filament voids, weakens the vapor-related convective component, and increases Ret; changes in filament-scale geometry mainly shift the balance between conduction and vapor-related transport when packing factor is similar; and twist further tightens the inter-filament void structure and strengthens these trends. Overall, the combined experimental–numerical approach links standard Ret measurements to fiber-level structure and offers practical guidance for designing PET yarn systems with targeted moisture management.