I needed to run a cat6 cable through an interior wall between the living room and the office. Upon removing the drywall to insert a low voltage bracket, I realized there was a thin, opaque, plastic cover between the drywall and insulation. There is a similar sheet on the other side. My immediate thought was it was some sort of vapor barrier, but why would it be between interior walls, and why so thin, and why on both sides of the insulation? They're is no plumbing in either room or run through the wall itself.

Photos below. Any idea what this could be?

from the living room side from the office side

  • 1
    As its purpose is soundproofing, some effort should still be made to tape around the cable to avoid crosstalk. Doesn't take much of a hole to ruin soundproofing, and outlets are notorious for causing soundproofing problems. Apr 9, 2022 at 22:36

1 Answer 1


That plastic is indeed not a vapour barrier (retarder).

It is more likely packaging or wrapping for the insulation inserted in the wall, like "Poly-Wrapped Fiberglass Batt Insulation"

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The wrapping helps contain the insulation material to keep it away from sensitive skin & lungs during installation. Or the wrapper serves as a vapour barrier which you do not require in that wall.

And the insulation there likely serves an acoustic purpose, not thermal, to keep joyful chatter and dish clattering away from quiet office work.

So yes, you can poke through it.

  • I think you're right on with your answer. But that first picture looks to me to be 3-6 mil plastic. I've seen enough of that stuff - all over my crawlspace floor.
    – SteveSh
    Apr 9, 2022 at 11:38

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