Key words: Physiological comfort, knitted fabrics, protective clothing Abstract. Thermal comfort of clothing is associated with the thermal balance between human body and the environment, and also a balance between the body heat production and the heat loss. During work activities performed in extreme hot conditions, the body produces substantial amount of heat energy which leads to raised body temperature. As a result the body perspires in liquid and vapour form to reduce the increased temperature. When this perspiration is transmitted to the atmosphere, the body temperature reduces. Thus the garments worn next to skin should allow the perspiration and heat to easily pass through them; otherwise the result will be a significant discomfort of the persons working in extreme hot conditions. Therefore, thermal properties and water vapour permeability of the fabrics used for the next-to-skin layer of protective clothing are very important for the maintenance of physiological comfort of workers. In the present study physical parameters, air permeability, porosity, thermal and water vapour permeability of six commercially available knitted fabrics of different fibre blends, different and knitted structures suitable for skin layer garments of protective clothing worn in extreme hot conditions were evaluated. The influences of fabric physical parameters, and optical porosity on thermal conductivity and water vapour permeability of fabrics were determined and correlation coefficients were calculated between these variables.