From BruMate’s Website: A new Era of straw tumbler is here. Our Era tumbler is totally leakproof, and made for stress free sips on the go. It has our fully leakproof Ü-Turn™ lid that works for both cold and carbonated beverages, ColdKey™ metal straw for minimizing the amount of plastic sitting in your water, BevGuard™ technology to keep ice for 24+ hours, and a cup-holder friendly base so you can enjoy 40oz of your favorite beverage, free of leaks and spills throughout your daily journey. Era Tumblers are 100% leakproof with cold beverages and carbonated beverages with ice when in the locked position. Not recommended to be used in the locked position with hot beverages.