It's so easy to put the batting and some of the thread in the microwave and zap for up to 3 minutes and see what happens before you sew. I had 100% natural cotton no scrim burn black in less then a minute. I always test the thread and batting first before using. The wattage of the microwave makes a big difference. Also a the dish used. If you dish gets to hot to touch in time for the food to warm, then it is not meant for the microwave.