I bought this to try out this summer, but I ended up not using it. However, I did confirm that it works, and it cools down incredibly well. It gets cold enough to be painful, so I think it's best to wear it over clothing like a T-shirt. This cool vest is equipped with a Peltier element cooling system and can cool down to -20°C, weighing a light 620g. While fan-equipped vests have become quite common, I think this Peltier element vest is the future. The elements are in three places as shown in the image, and it comes with a battery (6290mAh). The purchase price was about 15,000 yen. The box says the battery is sold separately, but I also purchased that separate battery (genuine product), so it's included. - Brand: EXFROZEN - Product Name: FROZEN VEST - Cooling Temperature: -20°C - Weight: 620g - Function: Cools instantly when switched ON