I cut some 4 inch squares of different battings and tested them in the microwave. One was 100% cotton and it burned and stunk horribly. The wool didn't even get hot but it was too fluffy for the bowls. I used warm and natural. Try a test on the batting before using. I heated the batting for 4 min. That is time enough to heat a bowl of food. If you plan on using the batting for cooking like in potato bags be sure and test heat it the same amount of time it will be used for.