Okay, I bought two of these the last time Woot had them. Sorry, but they are not very good for the intended purpose of my purchase -- keeping coffee hot, or, at the very least, warm.
They keep their word in terms of being leak-proof, which is good, but tepid coffee is not.
I even "prepped" the mug by filling it with hot, hot water, letting it sit for a few minutes, dumping the water and adding the very hot coffee. Less than two hours later, the coffee was luke warm, at best. Yuck.
Oh, and I live in South Florida, so it wasn't exposed to very cold weather. Buyer beware if your purchase is to keep liquids warm!