Now why would this be on an HVAC duct?
It wouldn’t be a half assed repair now would it?
Kinda looks like it.
Hope it vapor proof to keep it from raining inside the insulation.
Reminds me of the attic I inspected a week ago. The entire attic was carpeted with this heavy, mylar like foil. I’ve seen the foil backed roof decking and even foil on the underside of rafters but this was the 1st time I had seen this method used in my area. The 12" of blown in insulation under the foil looked fine. Quality of the photos is poor because the foil kept bouncing the flash and confusing my camera.
Look at it this way, new flex ducting is R6 to R8 at best. The ceiling insulation is R30 to R38. So, there’s always heat energy in motion with ducting.
So, in hot climates like AZ or TX, if you add a reflective radiant barrier on top of the ducts, you would be reducing the heat flow into the ducts. Just how much is debatable. The same is true for adding the same stuff on top of the ceiling insulation.
In CA, you can get extra credit on the Title 24 energy requirements if you go with “deeply buried ducts”. All the installer has to do is to add an extra 4" to 6" of blown in insulation on top of the ducts. Same prinicipal, more insulation to prevent heat movement.