Munchkin's Flip Straw Cups, which come with a 100 percent leak-proof guarantee. These innovative toddler cups feature an effortless locking lid with straw that closes to create a leak-proof seal. You can see, hear and feel the cup lock in place, so you have triple guarantee against dribbles and drips. Munchkin even backs this no-leak promise with a 100 percent replacement guarantee. Secured, and rest assured - this might just be the sippy cup of your dreams.