In case anyone is wondering what these descriptors (heavy duty, extra heavy duty) mean, according to this link below:

standard duty aluminum foil is between.0004 thick and .0007 thick
heavy duty is between .0008 thick and .001 thick
extra heavy duty is between .0011 thick and .0016 thick

http://www.uspackagingandwrapping.com/blog/Thickness-of-Aluminum-Foil.html