In this paper the thermal properties of cotton and polyester based single jersey of 1 x 1 rib and interlock structures were statistically investigated. The thermal properties of samples were measured using A lambeta and Permetest devices. The results indicate that each knitted structure tends to yield rather different thermal comfort properties. Interlock and 1 x 1 rib fabrics have a remarkably high thermal conductivity and thermal resistance value. On the other hand, single jersey fabrics have higher relative water vapour permeability values than 1 x 1 rib and interlock fabrics, and give a warmer feeling with lower thermal absorptivity values.