I have a house that was built in 1977 in houston which I bought last year. The AC system up until the boots/Register/vents were installed in 2007 or 08. and the Air Duct boot/Register/Vent ( I am not sure exactly what they're called) has insulation on the inside that has overspray from when they did the ceiling and mold present. I just removed the insulation which to me does not make sense, however I cleaned the area where the over spray occured with bleach and like I said removed the insulation on all of them and cleaned them with bleach. My Question is; Does this insulation that looks dirty and old need to be there? What purpose does it serve? I thought insulation is for the outside not inside your air system especially at the end where condensation might collect along wth mold.