EDIT:
There are some of the Michael Miller Fairy Frost fabrics that say they are 100% cotton (shipping June 15th); they are dimensional. Others are flat or dimensional & say they are pearlized cotton metallic -- which definitely would be dangerous in the microwave. -- or glitter, which has the potential to melt, fall off everywhere & generally make a mess (you know how I know). You can check by each color at:
http://www.michaelmillerfabrics.com/...iry-frost.html
The bigger question is how well that kind of fabric will hold up in the wash -- especially the multiple washings required of that kind of product. I usually go lower budget with that kind of stuff.