"Joseph" wrote in message
This is very likely an asbestos covering and should not be disturbed.
You may even want to have the ducts replaced, I would. The costs to have
it
removed are well worth it, as it is not worth the health risks having it
in
your house create.


Sealing makes sense. Removal is not needed as once the material is sealed,
there is no health risk. It is only the inhalation of fibers when it is
broken up, or cut, or otherwise disturbed that presents a risk. Touching
the stuff will cause no harm at all.