Bigborn AQUATEC Aqua Water Vest AT101 Cools the body using only the power of water, no battery required. Employs a uniquely developed evaporative cooling system. An aqua water vest that is also ideal as an inner layer for fan-equipped wear. 【Unique Evaporative Cooling System】 Utilizes the principle that when water evaporates (vaporizes), it absorbs heat from its surroundings, providing a long-lasting cooling sensation with just water. *The cooling effect is based on the principle of evaporative cooling, so it varies depending on the surrounding temperature, humidity, and wind strength. I purchased this online and used it 2-3 times, but it didn't suit me, so I would like to pass it on to someone who can use it. No instruction manual included.