At Wing On they have flasks/thermos' that are big enough to fit one of the larger 8oz bottles inside. We use these in the summer to keep my daughters night bottles cool and in the winter to keep them warm. If I pop a warmed bottle in at midnight it was a good drinking temperature when she needed it around 4 or 5am. Same for a bottle straight from the fridge in summer. Also good when going out in the day in summer. Although this was all with expressed breast milk, wouldn't be possible with formula.