Using radiant barriers as duct insulation, Aka "Bubble wrap" What value do you assign for R-value?

I recently inspected a house that I am rating and discovered the HVAC contractor used Big 8 bubble wrap on the metal main duct in a vented attic in Climate zone 5. I spoke to the contractor about this at the rough inspection and duct testing and told him he needed to add more insulation to the nice wrap job he had done. My experience has been that a materiel that thin + a thin air space can not be classified as a R-8. I found a few articles from some pretty knowledgeable building science guys to confirm my thoughts. The contractor however is insistent that this is a suitable method of insulating duct work. He sent me the manufacturers claims and I looked up a ESR -report. (ESR-1236).  First I must say I do not work on really any new buildings with duct work outside the thermal boundary and advised agaisnt it! 

What is the industry accepted method for crediting duct work wrapped with a radiant barrier and a airspace.?The ducts did pass a total leakage test, but they still leaked so, it is not in a vacuum either. I could not find any official language by RESNET or IECC on this.

Thanks for your Thoughts in advance!

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I think Ed and his video hit on an important point -- these radiant barriers are primarily addressing radiant energy.  They aren't doing much to address conduction losses and, if not installed properly, will not address convection losses.  And let's face it, its difficult and unlikely to get a "proper" installation in the field.

If you are still seeing duct losses, this bubble wrap insulation is not installed "properly" (i.e. the air leakage from the duct is also leaking out of the Big 8 Duct Insulation) and therefore will not be able to achieve the claimed R-value.

I’ll give you an a for effort but even in the best cases bubble wrap ( unless it comes with a certificate of testing and depending on what lab was used) means nothing.
If you can get a engineer’s stamp with signature maybe that might carry some weight, good luck
GP Master Hvac contractor

I believe one of the issues is how does one defend themselves against an HVAC contractor that insists it is okay.   And the answer to that would have to be pull articles from ACCA or AHRI which say that reflective bubble wrap is worthless for duct insulation.  Otherwise it simply becomes a dispute between the trades.

As an engineering type - I can argue that for duct insulation it is nearly worthless most of the time because the installers often don't understand the limitations and HOW IMPORTANT the strict adherence to the installation instructions are.  For example without the spacers and the 1" air gap all around the duct... the manufacturer's own claim for R-value drops from R-8 to R-6.

I really doubt that the installer is able to certify that the installation instructions were absolutely followed without any deviation. 

Also from about nine years ago - this discussion on greenbuildingadvisor

https://www.greenbuildingadvisor.com/question/is-bubble-wrap-duct-i...

At the time - not Energy Star approved and not approved for ACCA manual D.

On a tangentially related topic:

I saw this today in an old attic installed AC system. Ducts made from only fiber-board, coming apart at the corners.

If you look closely ... can you see rat or mice teeth marks on foil?   Some of the modern materials are gourmet meals for rodents.   E.g.  they really enjoy a snack on some PEX  or the insulation from some automobile wiring...

Hmm, good point. I didn't notice any droppings but it could be. I'll check my other pics.

Pests are also a really good reason to seal duct work with either the approved mastic OR aluminum duct tape... not the sticky "un-Duct" tape that DIYers use... "un-Duct" can be tasty for some critters...

To the right of your hand.... it looks like droppings...(?),  when I enlarge photo, it looks like chew marks.   

Also another reason to where mask when going up into an attic......

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