Best air duct insulation?

[RickM]

I have the typical sheet metal duct work for both A/C and forced hot air. In the basement the majority of the duct work is wrapped with a plastic that has a fiberglass lining. Well, I guess the method to secure is with string that goes through gromets. The string has broken in some spots and the wrap is kind of hanging.

Anyway, before repairing I figured I'd throw this out and inquire on other options for insulating the duct work? This wrap seems quite archaic. Maybe a spray foam or something along those lines.......

[mschuep]

Generally, spray foams are pretty expensive, and are used more frequently on surfaces within the space rather than on the ductwork itself. Sometimes you will see a fireproofing spray on I-beams and ductwork, but they don't do much for the efficiency of the system, or noise attenuation.

Nonetheless, the standard for spray-on type insulation for years has been K-13...
http://www.internationalcellulose.com/home/products/k-13/

If you are interested in general plenum liner board, or duct wrapping (lagging) I would check out products by Knauf or Johns Manville

Here is some typical lagging that might be used for general HVAC applications.
http://www.knaufusa.com/products/building_insulation/commercial_building_insulation/knauf_friendly_feel_duct_wrap.aspx

edit note: I usually reference these products for commercial applications, but I would imagine you could find stuff very similar at the local HD.

[RickM]

Matt, thanks for responding. My existing wrap look spretty much the the product you link to. Looks like I'll just use new string to resecure....or use some of the Tyvek tape. Other tapes just don't hold onto that plastic cover very well.

[competentone]

For the situation you describe, I normally use Reflectix insulation (available at the Lowes store locally in my area):
http://www.reflectixinc.com/script/products/product.asp?ID=72

I seal the lap seams with aluminum tape.

It's a LOT cleaner to work with than any fiberglass insulation. If most of your fiberglass wrap is intact, just re-wrap over it with the Reflectix.