The first morning I drank out of my cup, I bragged on it to my wife. She said "yeah, I was looking at it and it doesn't look very spill proof." I thought "of course it's spill proof, this cup got great reviews and how hard is it to make a cup spill proof? I mean, really!" So....I turned it over and got a lap full of coffee. Since then, it's been knocked over in the car when only about a quarter full....again spillage....I love the looks of this cup-it does an excellent job keeping my coffee warm but.....the closure is more of a suggestion than actually having any sort of closing/sealing function. I had a starbucks mug like this a while back and it was by no means perfect, but it didn't spill when turned upside down.