Different microwaves have different levels of power, so your microwave may burn something that is ok in someone else's microwave, so test it! I set s potholder on fire in the microwave. Was not nice.

I just made two of those bowls, and used Quilter's Dream all cotton. My directions said to use all cotton with no glues or skrim, which QD is. Haven't tried them in the microwave yet.

You need at least 2 layers of batting. I've used other things like old towels, and stuff like that. You do not want insulbrite with the metal in it to go into the microwave.

To the person who reported cotton burning in the microwave, if you put just the bowl holder in there without a bowl full of something, this is much more likely to happen.