My grandfather was a fireman, and the husband of one of my closest friends is a fireman. I would never put a potato bag, soup bowl kozy, or anything made of any kind of fabric (especially if you didn't make it and have no idea what the fabric and batting content is!) in the microwave. It is just too risky, no matter what your wattage is, no matter what materials you've used, etc. I bake naked potatoes in my microwave all the time, it has a "baked potato" button and they turn out perfect.