I didn't buy a thermos so the non-sip lid is useless to me. Unfortunately the sipping lid doesn't screw on so it can come loose plus the lid is not leak proof. Ember shouldn't call this a Tumbler. You can't treat it like all the other tumblers out there when traveling. You have to use it like any other coffee cup and always keep it upright and make sure it doesn't get jostled around in a bag. So the only "traveling" it works okay with is car traveling (assuming the very wide mug fits in your cup holder which it may not depending on your car).