Ok I have in the past made up formula and stored it at the back of the fridge which goes against guidelines but lots of us do it. However my friend makes up the formula and keeps it in a bottle warmer - a tommy tippee thing that looks like a cool bag with a zip and everything - it's material - but it;s supposed to keep the formula warm. So she makes several and then keeps them in the bottle warmers all day. She said it doesn;t keep them that warm just to room temp - so the milk is sat out all day at room temp. i did say that I thought you needed to fridge them immediately but she thinks not. I am wrong?