It is the vapor barrier.

I had to have the left rear door corrected twice. Mine had a small pin hole.

The second time the tech damaged the trim and I had to get it replaced. He used screw drivers to pry it off and dented the metal under the door handle.

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2007 4.8i, Space Gray, Dark Burl Walnut Wood, Black Nevada Leather

Packages:
ZCW Cold Weather, ZPP Premium, ZRC Rear Climate, ZSP Sport, ZTP Technology

Options:
217 Active Steering, 322 Comfort Access, 328 Running Boards, 496 Heated Rear Seats, 610 Heads Up Display, 655 Sat Radio, 840 Increased Top Speed to 150 MPH ,2LE 20" Y Spoke Wheels.

Mods:
Stainless Steel Pedal Pads