I personally would not use the microwave, but instead, what I do is make up all my bottles using cooled bolied water, but leaving space for adding some boiled water to bring it up to the temp I need, then add the formula and shake and go. But, what I do is just leave a small amount of water in my kettle, so it boils quickly. This works well for me at nights, when you need to get a bottle quickly. Not sure if this will help at all... Good luck... xo