The effect of the linear density, loop length, and blend proportion on thermal comfort properties (air permeability, thermal conductivity, thermal resistance, and water-vapor permeability) have been studied. Cotton, bamboo fiber, and blends of the two fibers (100 % cotton, 50:50 % bamboo/cotton, 100 % bamboo) were spun into yarns of linear densities ( $$20^{\mathrm{s}},\; 25^{\mathrm{s}},\; 30^{\mathrm{s}}$$ Ne). Each of the yarns so produced was converted to single jersey knitted fabrics with three loop lengths. The thermal conductivity of the fabrics was generally found to decrease with an increase in the proportion of bamboo fiber. The water-vapor permeability and air permeability of the fabrics were observed to increase with an increase in bamboo fiber content. An increasing presence of bamboo fiber in the fabric causes a reduction in the fabric thickness and mass per unit area for all linear densities of yarn. As the constituent yarn gets finer, both the fabric air and water-vapor permeability increase while the thermal conductivity decreases.