The influence of air gap thickness on clothing surface temperature is analyzed by means of experimental and simulated methods. A three-dimensional body scanner is used to determine the air gap distribution between different-sized garments. The clothing surface temperature is measured by an infrared thermal camera to evaluate the heat transfer through air gap layer. The combination of two non-contact measuring techniques is a novel way to investigate the relationship between air gap thickness and clothing surface temperature. A mathematical model is set up to simulate the heat and moisture transfer from skin to environment by including the sensible and latent heat transfer through air gap layer under clothing, fabric layer and boundary air layer adjacent to the fabric. The established mathematical model is used to forecast the surface temperature and evaluate the heat transfer capacity of different sized garments.