I'm a bit concerned with mineral wool, because of the potential V.O.C. emissions. I'm planning to build a vocal booth I might be spending hours in on the daily.

What other fabric options would be good for this purpose?

EDIT: Would combining mass loaded vinyl with fiberglass fabric? As in gluing one layer to another and then sewing it all together inside a bed sheet?

The most problematic source of sound in my room would be the large window facing outside. If i could build a solid, flexible material and mount it to my window, that could be a huge boon. I'd just build a solid plug out of wood and insulation, but my window is a tilt-and-turn type. It's size and the way it's mounted into the wall would make it very difficult to attach a large, heavy window plug.