Fiberglass or reflective roll insulation for duct work?
I prefer bubble wrap as it generally looks nicer and is easier to clean if looks are important. However the R value for single ply with no air gap is generally about R-4. To achieve R-6 you would need to provide an air gap by first cutting strips and then go over the strips with the bubble wrap. R-6 is generally considered the minimum. 2” faced fiberglass is generally R-6 as well.