I had many types of cotton batting. I cut a piece of each and put it in the microwave to test it. The warm and natural didn't even get hot after 6 minutes. The 100 % cotton started to turn black fast. None of the batting lasted up to 12 minutes in a microwave. Some microwaves are higher wattage then others so will get extremely hot faster. I use the microwave bowls to heat food not cook it. 3 minutes is long enough to heat soup piping hot with the low wattage ones. 1 minute with the high wattage.