Thermal manikins have evolved considerably for over 70 years. This sophisticated tool has become more and more popular and reliable when analyzing clothing characteristics in humans nowadays. However, many kinds of thermal manikin systems are varied in different designs, materials, and purposes. This study reports experimental research on a thermal manikin with 15 exothermic positions. The research aimed to evaluate the exothermic reaction of the upper human body using two different materials of shirts. During the experiments, the temperature from the manikin was controlled by a temperature sensors system and collected by Scada temperature software. The room temperature was unchanged during all the tests. Based on the decreased speed during over one hour on each exothermic position of the upper manikin body, there was a significant difference between using different materials including 100% cotton and mixed materials of cotton and polyester. In conclusion, the thermal manikin contributes to the confirmation of comfort level when using materials of 100% cotton compared with mixed polyester.