This is where the suede-shoe foil sales engineers and the R-value insulation salesperson clash.
The argument is based on how you rate R and what you get from foil.
Foil insulation reflects back 97% of RADIANT heat from its clean surface NOT IN CONTACT with a surface. However, duct work does not radiate much heat from its surface, or it would be useless trying to keep the air warm or cold as it passes through.
R-value is based upon the material being one-foot square and 1-inch thick. So if you want the full R-value of the bubble wrap, wrap it 1-inch thick around the duct. This would mean you need 4 or 5 layers of it to achieve the same as applying a 1-inch thick layer of the polyisocyanurate Hi-R foil-faced foam you can buy in sheets at building suppliers.
This would be the same as putting a 2-inch thick fiberglass wrap around the duct, but much less chance of cooling getting the fiberglass wet if the foam board is properly sealed with aluminum foil duct tape.