I got this mug from my brother for Christmas and have him every day on the way to work with me. When I arrive at the office, my coffee is only lukewarm (between filling and drinking is about 1 hour). In addition, not a day where I do not have to bend the finger when screwing passes. The surface is a little rough but there are no grooves or the like which one helps open. I need to open so always an eternity, and that's really annoying.