Facemask vapor trapping, condensation, and thermoregulation

•A computational model simulating mask-wearing was developed to analyze vapor trapping, condensation, and thermoregulation.•The model incorporated cooling/warming effects from breathing cycles, skin heat dissipation, tissue heat production, condensation latent heat, and moist air thermal expansion.•Model validation was performed using Schlieren imaging and transient under-mask temperature measurements.•Ablation studies were conducted, comparing scenarios with vs. without a mask, tidal vs. constant breathing, moist vs. dry air, and including vs. excluding buoyancy. The widespread adoption of facemasks in various contexts has highlighted challenges associated with prolonged mask-wearing. Despite their effectiveness in preventing the spread of pathogens, issues such as discomfort, stuffiness, and fogging of eyeglasses can deter individuals from wearing masks consistently. Understanding the mechanisms of thermal and humidity regulation during facemask use is crucial for addressing these challenges. This study investigates the impact of face mask-wearing on facial thermoregulation and moisture accumulation, comparing conditions with and without masks. An integrated computational model was developed to consider respiratory flows, tissue heat generation, skin convective heat dissipation, the influence of inhaled cool air and exhaled warm air, and their interactions with the mask media. Model validation was conducted using complementary Schlieren imaging and transient temperature measurements. Results reveal significant increases in facial temperature with well-fitted masks and highlight the role of trapped moisture inside the mask. Thermo-humidity variations beneath the mask and condensations in the mask were quantified, providing insights into facemask-wearing thermoregulation. The effects of moist vs. dry air, steady vs. tidal breathing, and with vs. without buoyancy were quantitatively compared. These findings have implications for improving mask design and promoting adherence in diverse environmental settings. Addressing these discomfort-related challenges is crucial for enhancing mask adherence and ensuring adequate protection.