Bubble-wrap style radiant barrier varies in R value depending upon its
use and its environment.
It's specifically designed to block radiant energy in the visible and
infrared spectra. At that task, good quality material can be around 97%
effective, and can show an "effective R" of up around 19. (It must block
97% to qualify for the name "radiant barrier material")
However, it degrades in performance if exposed to ultraviolet for long.
Its polyethylene overcoating becomes cloudy, and begins to absorb radiant
heat, rather than reflect it.
It's a poor insulator for the purpose of acting as a barrier between
different air temperatures, dropping down to an R-2 value in that
On Tue, 18 Sep 2007 14:43:01 -0000, "Lloyd E. Sponenburgh"
Then I gather, Foil Bubble Wrap Insulation is not effective for A/C
ducts, which are located in the attic. Temp there can be well over 100
degrees. Is this a correct interpellation? What is the best
reasonable priced material to use for duct work trunk lines?. I do
realize you get what you pay for. Thanks
You didn't describe the ducting. If it's made-up metalwork, you'd
_better_ get some insulation on it. Most residential work seems to end
up as flex or ductboard, primarily because it requires much less skill to
install than metal. Most installers don't have the skills to make custom
metal. Typically, they're using pre-fabbed components, and just hooking
Flex duct and ductboard are already insulated to one degree or another.
Older stuff was about R-2.5; new material is usually R-6.
You have two primary insulation issues to deal with, and an ancillary
one. The first is the air temperature in the attic. That requires
thermal insulation -- foam, fiberglass batt, or fiberglass pressed board.
The second is radiant (IR) energy booming down from the roof surface.
That requires a radiant barrier film. It's best placed on the underside
of the attic rafters, but flex duct can have it as the outer barrier
layer (Silvaflex, etc). Most ductboard typically has an aluminum radiant
barrier outer layer.
The third issue is to provide some sort of vapor barrier between the
potentially humid attic space and the cool outer surface of the duct
liner. Again, flex and ductboard accommodate this with the outer barrier
layer, which, if it's taped and mastic'd properly will keep out moisture.
Metalwork must be properly wrapped and sealed to prevent moisture
traveling to the cool surface, and condensing there. If the thermal
insulation layer gets wet, the R value essentially drops to nada in the
Commercial work in our area uses either a wrapped fiberglass batt topped
off with a continuous layer of mastic, or a spray-on foam material.
The foam is a superior insulator AND moisture barrier combined, but for
commercial installs (here), it must be covered with intumescent paint in
order to meet fire codes.
You have a lot of options -- but first it boils down to the original
question; What type of ducting do you have?
Yea, I can see that working. I went back to Google and found a few web
pimping their version of the product. Like you say, under a roof deck,
or stapled across exposed roof rafters, reflecting the radiant of a
Florida sunny day.
I recall the times I neglected to throw up my
foil-like windshield sun visor for the duration of a sunny day... and YES,
works VERY well for that application. I TRY not to let that happen
very often, though. :o)
Thje bubble wrap has an insulating factor of R-6 if I remeber correctly.
BUT---it has to be installed properly. Most guys just wrap it around the
duct. You have to properly install spacers between the duct and the
insulation. If you don't it aint worth shit. If they are going to use it
watch them, if not make them use an R-8 blanket insulation.
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