off gas?
703 and similar material is safe....no plastic that i know of will work...if sound can get in, then the supposed "off gas" can get out...so kinda pointless anways...
just wrap them in fabric and dont worry about it...
edit:
heres a thought...if you are worried about "off gas"..then let the insulation sit out in a well ventilated area for a week or 2 prior to wrapping/installing them