Thermal Comfort and Energy Efficiency of Intermittently Heated Protective Clothing in Cold Conditions

Balancing energy efficiency and wearer thermal comfort in cold environments remains a critical challenge for wearable heating systems. Commercial graphene-film heating pads, consisting of a graphene film sandwiched between cotton-gauze layers, provide a flexible heating platform; however, the effects of temporal power-modulation strategies on physiological responses, subjective thermal perception, and energy use remain insufficiently understood. Using identical heating elements and fixed heating locations, this study evaluated three intermittent heating strategies for electrically heated garments: (i) a descending-step protocol (IP-1), (ii) alternating dual-power heating (IP-2), and (iii) periodic ON/OFF cycling (IP-3). Ten healthy male participants completed five randomized experimental conditions, including continuous heating (CP) and no heating (NH), during 60 min of exposure at −5 °C. Mean skin and torso temperatures, together with subjective thermal sensation, comfort, and preference, were assessed. Compared with IP-3, IP-1 and IP-2 maintained significantly higher mean skin temperatures from 15 to 60 min (p < 0.05), while their subjective responses remained closer to thermal neutrality. CP produced the strongest local warming but resulted in excessive warmth in the directly heated torso regions, whereas IP-3 provided insufficient thermal compensation. IP-1 achieved the most favorable comfort–efficiency balance, maintaining torso warmth and acceptable subjective responses while reducing energy use by approximately 46% relative to CP. These findings indicate that the transition characteristics and continuity of power delivery, rather than heating duration alone, are critical for optimizing thermal comfort and energy efficiency in wearable heating systems.