I truly love the Ember 2 mug, I bought two over the past 5 years. I was excited when I came to purchase my second and saw this genius sliding lid. What a great way to keep it hotter longer! (As one of the weaknesses in my mind is that the battery life is not awesome away from the charger.) HOWEVER it doesn't fit. Like, every time you pick it up to sip you have to press the lid back down and it immediately pops back up again. If you're not careful you'll spill coffee all down your chin/neck/chest. I found myself trying to explain this huge failure - maybe it expanded because it's hot? Maybe because it's wet from the coffee? But one would expect a custom lid made for the Ember 2 mug to fit tightly when it's hot and full of coffee. It needs re-engineering, I had high hopes but unfortunately only used it once and would not recommend.