We collect used coffee grounds from bars that repackage them in the old mylar coffee bean bags. We now have a 33 gallon trash can full of these leftover bags. I thought about sewing them all together into a giant quilt to insulate a roof or something, but will the grease from the old grounds in the bags cause problems in the future? Mylar use keeps growing while methods of recycling it do not. To end on a positive note, here is a plastic bag upcycle movement for communities that makes multipurpose blocks http://www.wastedlab.nl/en/