hvac duct insulation

The hvac supply ducts in my attic are insulated and have a black cover. The ducts in the basement have a silver cover. Is this normal? Or does it matter? I would have thought that the black covered insulation in the attic would absorb attic heat and increase the temperature of the air supply.
-Jim
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Is it Flex duct?

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Yes.
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Some flex has got a plastic vapor barrier and some has a metalized barrier....
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Would one be preferred in an attic over the other?
Thanks for replying.
-Jim
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Jim wrote:

Flex duct is not to be preferred period. But to answer your question: It's the R value that matters, not the color.
hvacrmedic
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RP, Flex duct is easier to seal and usually performs better thermally. Sheet metal will pass more air with the same static pressure. Flex duct is quieter.
It is a trade off, depending on your situation.
With sheet metal, to have a tight system, you must seal every gore on every elbow. You must seal every joint in the duct, plus you must seal every longitudinal seam. Then you hust do the same thing with the wrap. And if you install the wrap tight so it looks nice, the actual R-value is about 1/2 rated value.
With flex duct, you just have to seal the connections at the ends, but it must be supported at closer intervals with wider straps. But you get full rated R-value for the entite length.
Stretch
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Stretch wrote:

Which is why it isn't legal here except for drops.
hvacrmedic
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This is Turtle
if I was going to use Flex Duct. It would be the Black for it is made to be sun resistant and not crack or fall a part like the silver will in sun light.
TURTLE
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Thank you all.
-JIm
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Stretch and RP answered before I could and their answers were the same mine would have been.
I don't really care for flex because of the way it's usually run. It also has a higher resistance than the same size hard pipe.
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Timely question. I wanted to insulate the ducts in my garage. Have seen the black, but wondered it it's just garbage bags or sheet plastic stapled over normal attic fiberglass R11 or similar.
Anyone have a suggestion on what to use? Mine are normal galvanized ducts, some rectangular and some round.
Local Home Depot looks at me funny, when I ask about it.
Rich
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