I don't like the wrap-n-zap. I think it is too thick. I found some 100% cotton batting with cotton scrim at JoAnn's a few weeks ago. I tested it and it seems to work fine. I always test and make sure people know to only microwave them 2 minutes at a time at most.
However, I did buy some 100% wool felt that seemed like it might be the right weight. I haven't used it yet, and I think it was a little expensive. But I was thinking wool doesn't burn, but will smoulder.
Has anyone tried wool for bowl cozies?