My wife has had one of these for three years now. In addition to being spill-proof, I would also say that it is almost bulletproof. Hers has been dropped, thrown, rolled, and tossed around in bags, cars, trains, etc. and looks almost like new. Also, the inside truly resists smells. Hers has been used for coffee and for tea, and as long as she washes it with soap once every couple of uses, the smell doesn't stick when she uses it with water. Just an incredible product that, especially at this price, is well worth the cost.