We noticed we had mold on our register grills due to one of our AC unit not draining anymore in the attic (water was ponding in the pan); we had a remediation company come out and they told us we needed to change the one unit and all the ducts; then we had to clean the ducts on the second unit and change the insulation in the vent registers; not cheap, to say the least. we ended up replacing the entire unit and all the ducts attached to that unit and we did the duct cleaning on the other unit. But we decided to replace the insulation on the vent registers ourselves. Unfortunately, to find out that we don't know where to find this type of insulation (3" wide); we googled and researched, but not much info on what type of insulation we need to use and where to find it. I went to an AC supply store and was told to get some "black" insulation (soft on one side with a harder film/felt on the other). The previous insulation was yellow with paper on one side. does anybody know if any insulation can be used for that purpose ? can this "black" insulation be used ? any input would be appreciated.