YOu can't put warm and natural in the microwave. It has a polyester scrim which can catch on fire in microwaves with high wattages. The Warm company made a special 100% cotton batting that was made specifically for this purpose 'something tater' but discontinued it. Their new 100% cotton batting is called warm & plush.
Pellon's version is called 'wrap & zap'
http://www.joann.com/pellon-wrap-n-zap/10706869.html