A testing chamber was designed to evaluate the performance of microclimate cooling systems, which are used to extend human performance duration in heat stress environments by flowing fluids through flexible tubing in a conforming garment, carrying excess heat away from the wearer. The flexible experimental system accommodates changes in materials and garment design. In this study, one side of a chamber was able to output heat at a rate equivalent with that of human; a second, opposed chamber controls ambient conditions experienced by the garment. Temperature changes in both the interior and exterior sides of the chamber were measured. The cooling garment was tested at different conditions, transient and non-transient styles, with and without flowing fluid, and at various wattage densities (367.3 W/m2 and 576.8 W/m2). The designed testing chamber was validated for proper functionality. It was observed that, having a flowing fluid through the garment was more effective at higher body temperatures (∼45 °C) carrying away the excess amount of heat from the body.