The heat and mass transfer through the garment to maintain the heat balance between the human body and the environment is dependent on the air gap thickness underneath the garment, which in turn is affected to a great extent by the body movement. Therefore, in this study, 3D garment simulation software was quantitatively validated by comparing the air gap thickness results obtained for stationary postures simulated by 3D simulation software and measured with 3D scanning method. The aim was to assess the capability of 3D garment simulation software to accurately determine air gap thickness distribution. Moreover, the effect of differences between air gap thickness of real and virtual garments on the thermal resistance of the garments was evaluated for individual body regions. It was found that the agreement between the two methods was within the range of 10 mm for air gap thickness. This difference resulted in small differences in thermal resistance for tight (up to 0.025m²K/W) and loose fit (up to 0.013m²K/W).