So I was a Skeptical with this but bought it because we had a need for it. You basically fill it up with hot/boiling water before you leave and it keeps it hot until you need it. I used the Keruig to fill it up. When we needed it the water was VERY hot. It warmed the bottle fairly quickly. I then put the water back into the thermal and used it hours later and again it was VERY HOT. So it was worth the money!