Let's keep it simple: this tumbler doesn't leak. The silicone sipper spout has a built-in valve that stops water from flowing when no one is drinking, so it's easy for children to quench their thirst but won't make a mess if the tumbler is tipped over. It's the perfect choice for active kids, or young ones just graduating from sippy cups who aren't ready for an open-topped tumbler yet. The 15-ounce tumbler is made of durable plastic, which is lightweight, sturdy enough for everyday adventures, and completely BPA free.