These leak as a cold (refrigerated) liquid inside comes to room temperature. The liquid comes up through the straw and spills out. (They also obviously leak when laying on their side, but I was surprised that they leak standing up at times.) Also, the top (colored) straw component is very hard to weave back into the top. After weeks of frustration, I ultimately leave that part in the top, pull it out only slightly, and hope for the best in terms of cleaning.See full review