I loved the sippy cup in this line so much that I decided to buy this one for my toddler. It is anything but leak proof. This cup is more like leak prone. I am considering returning it, but I got it on sale so what can I say. If my son does not close the lid, and what toddler remembers, it leaks slowly on it's side. I'm sick of puddles and now will not put juice or any other non water substance in it. It will remain a secondary sippy cup for travel and home. It is easy to clean and very durable. The outside is the same basic design as the first in this line up. Therefore, I know it will last a long time, if I do not get sick of it first. I am sure the plastic on the bottom will fall off like the other one being knocked around and dropped. However, if there is one thing I like about the Thermos design, it is that it will keep my sons water cool on long hot days. There is nothing better than cool water, even for a toddler.