C.W.
I have had 2 different types (can't remember the names...sorry!) and I found that everntually they DO heat the bottle up, but its not instant...and usually you don't think to make the bottle until little one wants it, like now! So my suggestion is think ahead and start warming it early. We found that it would take 20-30 min of driving with it on to heat the bottle. A thermos works well though too (which I see many other requests mentioning) Good luck!