In this work, we proposed and evaluated the design of a suit to regulate the thermal comfort of astronauts for outdoor activities on Mars. The key feature is the incorporation of reusable packets of phase change material (PCM). The PCM acts as a buffer that enables the body to reject heat for longer periods of time. The PCM undergoes transition from solid to liquid near a comfortable skin temperature to help maintain the skin at a comfortable temperature while the phase change occurs. Although many more considerations for the full comfort of a Martian astronaut must be considered (e.g. pressurization) this work focuses primarily on regulating the thermal comfort.