Walmart carries the 100% cotton microwavable batting.
https://www.walmart.com/ip/Wrap-N-Za...llon/213705608
I use 100% cotton thread and fabric too. We don't put ours in the microwave, but I make these for other people that might put them in the microwave. BTW, here is a link to Tamarack Shack's pattern that I use:
http://tamarackshack.blogspot.com/20...-tutorial.html
I changed up the center to reflect quilted circles. These are such great Christmas gifts and fun to make.
Annie