There are several different products.
I have used the "bubble wrap" stuff. It's just your plain old bubble wrap
(1/4" bubbles) with Al foil on each side. I have used it around HVAC ducts
that pass through un-conditioned space. I have also used the same stuff to
help "seal" the joists ends where they go over sill plates in the basement.
I don't know if it's the same company but the bubble wrap stuff (and the Al
tape) are sold at HD or Lowes' (don't remembers which).
The other stuff is just for radiation barrier only. One type has holds for
water vapor to pass through and the other doesn't.
If you use the stuff which also serves as a vapor barrier you have to use
the tape to stop any leaks. Otherwise, the tape just helps to keep
overlaps looking neat.
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