Funny I seen this thread. My mom has a sinus infection so she has been using a rice pack made out of two washcloths on her face. She came to my house yesterday and put it in the microwave, she pulled it out (after about 30 seconds or so) because it started smelling like burnt popcorn! there was a hole burnt all the way through both washclothes! so BE CAREFUL with rice backs!
I too have used 100% cotton and never had a problem but I guess there is always a first time for everything.