Let's keep it simple: these tumblers don't leak. The silicone sipper spout has a built-in valve that stops water from flowing when no one is drinking, so kids can quench their thirst without the mess if it tips over. Perfect for car rides, park days, daycare, or home. Ideal for active kids or young ones just graduating from sippy cups. This Kelso Blippi set includes a stainless steel insulated tumbler that keeps drinks cold, a lightweight plastic tumbler, and a bonus sipper spout.