Best products to insulate rigid metal AC ductwork

[Andrew S.]

I have a fairly long stretch of rigid metal ductwork in he crawl space of an mid-50-ies property. Just blank metal.  I suspect I have substantial energy losses because of it, but even worse, humid Summer weather is closing in and I bet I'll get water condensate like crazy.

So, I'd like to insulate this ductwork.  Are there any special products out there for this purpose or should I just try to wrap things like water heater blankets as best as I can?  Does anyone have experience with this?