Measuring the Heat of Wetting of Clothing Fabrics by Isothermal Calorimetry

The interaction between moisture and textile materials plays a critical role in transient thermal comfort, particularly through the exothermic heat released during wetting. While the heat of wetting has been extensively characterized at the fiber level, its behavior in finished fabrics, where structure, porosity, and air gaps influence moisture uptake, remains poorly understood. This study quantifies the heat of wetting of clothing fabrics using a TAM Air isothermal microcalorimeter under controlled isothermal conditions (23 °C). Five fabric types representing different fiber chemistries (Merino wool, cotton, viscose, and polyester) were evaluated in both folded and dissected forms to assess the influence of sampling methods. Wool fabrics exhibited the highest heat release, followed by viscose and cotton, whereas polyester showed negligible exothermic response due to its non-hygroscopic nature. Overall, fabric-level heat of wetting values were lower and more variable than the corresponding fiber-level values reported in the literature, reflecting the combined effects of fabric structure, air permeability, surface hydrophilicity, and sampling uniformity. These findings demonstrate the feasibility and limitations of isothermal microcalorimetry for characterizing moisture–fabric interactions and highlight the need for improved sampling and measurement protocols to more accurately capture fabric-level sorption heat relevant to clothing comfort.