I only tried it on once. I bought it at Workman for 16,800 yen. This is the Iceman Inner Vest, which is useful in the hot season. It's a vest that uses a water-based cooling system to easily keep your body cool. - Product Name: ICEMAN VEST - Battery Capacity: 3350 mAh - Cooling Method: Water-based cooling system - Set Contents: Vest, Battery Size: Free How to use: ① Fill the tank on the back with about 150ml of cold water. ② Put a frozen PET bottle or ice in the tank on the back. ③ Turn on the battery. I have tested the water flow during the fitting. I have checked the battery charging and pump operation. I am selling it because my environment has changed and I probably won't use it in the future. Thank you.