Chamber with the controlled temperature is required in the energy efficiency test of a household product. Chamber wall plays an important role to keep the temperature inside the chamber so as not to be affected by the temperature from outside. Experiments were carried out to compare the thermal performance of two different material for chamber wall : 1) Acrylic and 2) expanded polystyrene. The boxes with dimension 40 x 40 x 40 cm were affected with fixed thermal loads in a climatic chamber. Meanwhile, temperature inside the box was monitored with data logger. The thermal loads for testing were 40°C, and 60°C. Based on the measurement, temperature in the acrylic box reach the load temperature from the outside and starts steady at 300 seconds, while the expanded polystyrene at 550 seconds. The result show that the insulating performance of expanded polystyrene is better than acrylic. The result of this study can be used not only for refrigerator manufacture, it can also use by another industry related to thermal dynamic. The industries include aeronautic industry related to aircraft wall coatings for external temperature protection, building industry in terms of building wall coatings to maintain temperature stability, and other related industries.