I love, love, love these mugs.  I was so tired of my morning tea cooling before I had a chance to finish it.  The double glass walls of this mug keep liquids hot for a longer period of time.  I just pour water in, heat in the microwave and enjoy my tea to the very end.  It is suggested not to use a metal spoon for stirring.  I purchased heat tolerant, non-metal spoons which work very well.