This FLASK is made of double-wall 304 SS and adopts vacuum insulation technology, which can keep hot for 24 hours and cool for 36 hours. It can hold 4L of beverages or water, making it very suitable for people who engage in long-term outdoor activities such as long-distance driving, fishing, traveling, and camping. This flask has a cup at the top, so when you feel the water inside the bottle is too hot, you can pour it into the cups to cool it down first.