vacuum flask, also known as a thermos or thermos flask. It is an insulated container that is designed to keep drinks hot or cold for long periods of time.

The flask in the image is made of stainless steel and has a capacity of 4 liters. It has a handle for easy carrying and a stoppered lid to prevent leaks.

Vacuum flasks work by creating a vacuum between the inner and outer walls of the flask. This vacuum prevents heat from transferring from the inside of the flask to the outside (and vice versa) by conduction, convection, or radiation. As a result, the contents of the flask can stay hot or cold for many hours.

Here are some of the benefits of using a vacuum flask:

• Keeps drinks hot or cold for long periods of time: This can be helpful for people who are on the go and want to keep their drinks at the desired temperature.
• Durable and easy to clean: Vacuum flasks are typically made of stainless steel, which is a durable and easy-to-clean material.
• Leak-proof: Most vacuum flasks have a stoppered lid that helps to prevent leaks.
• Portable: Vacuum flasks are typically lightweight and portable, making them easy to take with you on the go.