Duct insulation has metallic foil facing to protect the fiberglass insulation and to reflect heat. Wall insulation is not suitable for this purpose.

one layer R-8 duct wrap.

ducts mastic sealed, all joints, long seams and 90 degree ells mastic sealed priot

to wrapping with duct wrap.

duct wrap secured with duct staples and fsk tape (foil scrim kraft tape...just like silver on duct wrap.)

this is the correct long lasting way to insulate ducts.

adding two layers of duct wrap, or putting wall/attic insulation over wrapped

ducts will result in condensation between the vapor barrier of the duct wrap

and the added insulation.

wet insulation has little to no insulation value.