If you make fabric items for the microwave you have to use the batting made to be used in the microwave. Some microwaves are more powerful then others. One minute in a powerful one can start a fire with the wrong batting. 100% cotton has scrim (a very thin layer of poly. Unless it says no scrim it has scrim.) A fast warm up probably wouldn't matter but when baking a potato for 5-6 minutes, it could start a fire with regular batting.