Effect of Air Permeability of Material and Structure of Air Layer on Garment Insulation

This study investigated thermal insulation in layered suit systems by systematically varying air-layer thickness and structure (single vs. sandwiched), fabric air permeability, and ambient airflow. A hot plate based apparatus equipped with air-layer spacers and an airflow-generation system was developed, and suit fabrics with different air permeability but similar thickness were fabricated. Heat flux from the heated plate and air-layer temperature were measured in three experimental series. Under no-airflow conditions, insulation was maximized at a 20 mm air layer, whereas a 30 mm air layer increased heat flux, suggesting buoyancy-driven convection. Under airflow conditions, thinner air-layers allowed airflow to influence the hot plate region more directly, while thicker-layers attenuated this effect. The sandwich-structured air layer reduced heat flux compared with a single air layer of the same total thickness, and its effect depended on the thickness distribution between the upper and lower air-layers. Fabric air permeability increased heat flux mainly under airflow, indicating that permeability effects should be evaluated under combined conditions of ambient airflow and controlled air-layer configurations.