The plastic surround isn't sealed so coffee would get caught within it. It was difficult to screw together and apart. Then, after a month of use (used maybe 2 or 3 times a week), the whole thing broke with the plastic surround completely separating from the mug part, and therefore the lid couldn't be unscrewed so it's sealed closed. Plus because the lid pushes into the cup to close, rather than screwing onto the outside, it means that it was easy to overflow it. Bought two and very disappointed.
