Research to develop environmentally friendly cooling systems continues to be carried out. One widely studied eco-friendly cooling system is the thermoelectric cooling (Thermoelectric Cooler/TEC) system. This study aims to determine the effect of cooler box wall thickness and device operating time on cooling performance (COP) and temperature inside the storage room of a TEC1-12715-based cooler box. The study utilized a two-factor factorial Randomized Block Design (RBD). The first treatment consisted of three variations of styrofoam wall thickness, namely 2 cm, 4 cm, and 6 cm. The other treatment was the device operating time with periodic recording intervals of 20, 40, and 60 minutes. The storage room of the cooler box had a volume of 17.5 liters. Observations were conducted for 60 minutes by measuring the temperature inside the box and electrical parameters such as DC voltage and current. The results showed that the factors of box wall thickness and operating time separately had a highly significant effect (p < 0.01) on the COP value, but their interaction had no significant effect (p > 0.05). Thicker box walls led to a decrease in the COP value; conversely, longer operating times increased the COP. The significantly highest COP value was obtained at a wall thickness of 2 cm with a value of 0.123. An increase in the cooler box wall thickness caused the storage room temperature to become higher. The lowest storage room temperature was obtained from the 2 cm cooler box wall thickness treatment, which was 16.3°C. (Roboto10 pt, Justify, Italic).