Can you use black or clear plastic on ductwork?

I have a main trunk supply line that is round and 16 inches in diameter. My return line is also that same size. I am thinking about wrapping the ducts with r-13 and using a black or clear plastic from Lowes to wrap on top of the insulation as a vapor barrier. My ductwork is in a crawlspace. I really don't think the kraft paper faced insulation is a good idea due to fire/et c.
I know I can buy special insulation for ductwork, but it is more expensive and does not give as high of an r-value.
Is this advisable/doable? If so would you use clear or black plastic?
Thanks for the help!
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No, no, no. If you use clear it will be invisible and if he is crawling around down there he'll run the risk of bumping his noggin because he won't see it. What would you do if I wasn't there to keep you on the straight and narrow?
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the more interesting question is on which side should he place the vapor barrier
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On Fri, 22 Jul 2016 09:15:41 -0700 (PDT), snipped-for-privacy@yahoo.com wrote:

You mention fire considerations. Ever see how hot plastic burns? I'd use a foil barrier
You can get some info here too http://www.iklimnet.com/expert_hvac/insulating_duct.html
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