This is the choice: either it is used in bath mode to warm the bottle filled with water, either in fashion thermos of hot water that is poured into the bottle and which is full of water tempered to reach the right drinking temperature. For my part, I am convinced by the brand Tommee Tippee, who developed the perfect bottle of systems, pacifier, doser. Again, I recommend one of their products, very well thought out, and just as useful as bottle warmers systems of other brands working trip cigarette lighter, or with a rechargeable battery system by using boiling water or using steam in an electrical sterilizer. I have them all ... The active moms will understand me!