I am amending my original review. 

We have used these now for a few weeks and they DO keep our coffee and tea warmer longer. Even the first five minutes in another mug the temperature will decrease from hot to warm. Not in these. They are very lightweight, which in my book is a good thing, but if you are envisioning a heavy glass mug, these are not that. We are very happy with them. And if we lose any to breakage, I am known for dropping and breaking glasses, we will purchase more. Love them!