I use the munchkin bottle warmer. I tried using the plastic bottles at first (medela and dr brown, but the temp did not go past 160. So I tried a relish jar from a suggestion on google, and it cracked after a few uses. Then I tried evenflo glass bottle, and it cracked after I put cold milk in. So I bought another evenflo, but this time it cracked after putting normal milk in. The crack rate is about 1/8. I am about to cry. Please help!