Stashelf is correct 100% cotton for fabric and batting. I use warm and natural. Bought a cheaper brand at A.C. Moore, I was not pleased with the results at all. I have made over 30 bowl covers in different sizes, and the ones with warm and natural batting are the best. This a good way to use those small pieces of batting in your stash.

I use 100% cotton fabric, batting and thread...never had a problem and have used them for several years now

I use 100% cotton batting, thread and fabric. I give as gifts. I wanted to make sure there wouldn't be a problem with them overheating. I would feel horrible if a fire occurred while someone was using one. Just saying!

Never walk away from your microwave when you're using anything like this, even the wrap and zap. If you are giving for gifts I would only use the wrap and zap because you can't control other people and the last thing you want is a fire in their home. That's what my friend uses for them with a big warning on a card.