I prepare my morning coffee. The cookie at the office because I have no time to waste to go to the coffee machine. At 10 pm, it is warm. At 14 pm, it is always at the same temperature. In the evening when I get home and remains of it, it is almost as warm as the morning! So life is good! And to optimize the heat, I poured boiling water overnight in the bottle. But I think qque absolutely superfluous.