I typically put a plate on top. Wouldn't trust paper or cloth to not ignite in the microwave?! At least my gf thinks I'm crazy to put things in the microwave that contain cloth or paper at all, and I don't know that it's safe for more than a few seconds. Food that I store in the freezer in glass containers typically needs heating for at least five minutes, usually more depending on amount
I can verify that paper towels will not combust after multiple minutes in the microwave. I usually dampen a (clean) hand towel to wrap/steam tortillas (under 40 seconds) and have never had an issue with that either.
I'm not sure that a dry cloth has enough microwave cross section (for lack of the proper term) to heat significantly, and a damp cloth therefore wouldn't go above boiling point. I'll experiment in my cheap office microwave.
Why do you think a paper towel would ignite? This has never been an issue for me. I use a paper towel which often times I can use for my hands or mouth after eating.
