Although the leak proof aspect will not last forever, it is by far the best sippy cup ever. I have had mine over three years and at least two of my three children have used it. It will remain leak resistant as far as I have seen. It is one of the easiest to clean. Other sippy cups always seem to build up yucky residue in spots that are hard to clean, but not this cup. It's durable design is unmatched. And it keeps the drink at a cool temperature even on hot summer days in the car. Ever take a swig of you kids sippy cup on a day of shopping to find it is unbearably warm? Try it with a cheap uninsulated one and you will jump to buy this. The little plastic part at the bottom did fall off after awhile, but nothing a little glue will not fix. My one son chews on everything, including sippy cups. He has ruined a few because of it, but not this one. The hard plastic mouth piece prevents this. It is well worth the money!