Enhancing thermophysiological comfort in defense clothing for hot climate: A comprehensive evaluation and introduction of passive cooling vests as a solution

Protective clothing systems pose significant heat stress challenges in hot climate, limiting natural cooling through sweat evaporation. In such conditions, passive cooling systems could offer lightweight, silent, and energy-efficient solutions. However, their effectiveness and their physiological and psychological impact are influenced by specific operational conditions, including the type of clothing system used. This study assessed the thermophysiological effects of three passive cooling vests - Phase Change Material (PCM), Waterfill (WF), and Watersoak (WS) - worn under Belgian Defense clothing system with ballistic protection during wear trials at 30°C, 48% RH, 4 km/h, 120 min. The PCM vest with a transition temperature of 29°C provided the most effective cooling, significantly reducing torso microclimate temperature for 60 min. Over the total test duration, the torso microclimate temperature was lowered by an average of 1.5°C, accompanied by reduced cardiovascular strain, sweating, and enhanced thermal and wetness perception. Thus, the PCM can be a better solution than active cooling for operations up to 2 hours. Water-based cooling vests delivered mild cooling, with significant effect at 30 min, but temporary duration. They still showed reduced microclimate temperature by 0.5°C at 60 min, but became a thermal burden thereafter, confirming their limited performance under restrictive clothing. The results also showed that subjective experience did not fully align with objective data, confirming the importance of individual perception in comfort-related studies.