The comfort properties of the underwear are one of the most important aspects affects human satisfaction while wearing clothes. Since most of the researches which study the comfort underwear properties concerns about either moisture management properties or thermal properties. In this study both thermal properties and moisture management properties were studied. The relation between constructional parameters and some physical properties on the following comfort properties (air permeability, water vapour permeability, thermal resistance, thermal conductivity, and vertical wicking time in both wales and courses directions) were studied for three single jersey knitted fabrics produced from different yarn materials 100% cotton, 70% bamboo/30% cotton, 100% bamboo on two machine gauges 24inches, 28 inches in attempt to determine the most suitable fabric for underwear. The same yarn count Ne 30 were used for all materials. Each fabric is knitted with three different loop lengths Tight, medium, and loose structure. It was found that loop length is a significant factor that affects air permeability, and water vapour permeability. Vertical wicking time in both wales and courses direction positively. While it has negative effect on thermal resistance. Fabrics with the highest loop lengths (loosest fabrics) have the highest air and water vapour permeability, and the highest vertical wicking rate in both wales and courses direction, while they have the lowest thermal resistance. The type of fabric material has a significant effect on air permeability. Water vapour permeability, thermal conductivity, vertical wicking rate in both wales and courses directions. 100% Bamboo fabrics have the highest air permeability, water vapour permeability, thermal conductivity, and vertical wicking rate in both wale and course directions, then comes 70% bamboo/ 30% cotton then comes 100% cotton fabrics. Thicker fabrics have lower air permeability and higher thermal conductivity. Machine gauge interacts with loop length and affects vertical wicking rate in both wale and course directions. Also, the machine gauge affects water vapour permeability and thermal resistance. Fabrics produced on a machine gauge of 28 inches (tighter fabric) have lower water vapour permeability and higher thermal resistance than fabrics produced on a machine gauge of 24 inches. It was found that bamboo and bamboo/cotton knitted fabrics are more suitable for manufacturing underwear than cotton knitted fabrics.