I only had one batting catch on fire. I didn't try poly. This was years ago when bowl cozies were first talked about. It was 100% puffy cotton batting . When Wrap and Zap batting was available I used that and never worried about it going in the microwave. Many thought it was too expensive and still used batting scraps and of course some did burn. Follow the instructions on the Wrap and Zap package and enjoy the bowl cozy.