Found this "tumbler" to be downright dangerous. When you fill it with hot coffee and put the lid back in place, the heat inside causes pressure to build up and consequently pushes up on the lid. Needless to say if you're not aware that the lid has come loose, and you're driving down the road taking a sip, you'll have scalding coffee dumped down the front of you. The lid is designed with nothing more than a thin rubber membrane around the outer edge for retention, and does not screw into place. In addition to this, the lid has no vent hole to allow the liquid to flow out evenly, and therefore only comes out in drips and dribbles as air might find a way in through the mouthpiece.