Read somewhere that with 100% cotton batting, fabric & thread, you still need to limit the time in the microwave to under 8 minutes -- and NOT use the bag again until after it cools all the way down. Made my own, it's all 100% cotton, and use it for 2 medium size potatoes only -- with a 1000 watt m/w, it takes 5 minutes, let sit in bag about 5 more. Wash, but hang to dry. So far so good...