I was instantly wow'd when I realized that the coffee I had poured into my mug at 6 am was still just as hot at almost 4pm when I was getting my son off the bus!  So I kept thinking maybe I should keep pushing the time to see how long it literally stays hot.... I got up to 12 hours before I emptied it to wash it for the next day!  Outstanding!  Now I use it all the time for my coffee in the morning!