Assessing thermal resistance of a nonwoven textile under wind exposure: Challenging ISO 9920 with experimental insights

Numerous workers across various industries, from construction and transportation to agriculture and emergency response, face harsh working environments characterized by cold temperatures and intense winds. These conditions present serious health and safety risks, which may result in hypothermia. Although established standards, such as ISO 11092, are crucial in measuring the thermal resistance of textile assemblies, an essential factor is often overlooked: the influence of wind speed and direction. In this context, this article aimed to address this gap in current knowledge by investigating the effects of wind on the thermal resistance of nonwoven textile assemblies, to develop a more effective protective clothing system for harsh environments. This study investigated the effect of horizontal and vertical wind speeds on the thermal resistance of a technical bio-based nonwoven assembly, composed of milkweed, kapok and polylactic acid, aiming to understand how forced convection influences heat transfer in real-world conditions. Three samples (A, B, and C) were tested under wind speeds ranging from 0 to 4 m·s⁻¹, and their thermal resistance was measured in both horizontal and vertical wind directions. Results showed that increasing wind speed consistently decreased thermal resistance for all samples. Vertical wind demonstrated a more pronounced effect, with reductions in thermal resistance reaching 81% for Sample C compared to 51% under horizontal wind. Comparison of experimental and theoretically predicted thermal resistance values using the models presented in the ISO 9920 standard, indicated significant discrepancies.