Does vapor barrier really do any good?

[autobonrun]

While trying to fix my slow power window, I noticed the techs left the vapor barrier off my doors when they installed speakers. Unless there is a major leak into the door, does this piece of plastic really perform any function? I know it's easy to replace but I'm interested just from a technical standpoint.

By the way, I thought the problem with my window raising slowly was the felt on top of the door. It turned out to be the teflon slide mechanism that lifts the window needed lubrication. I know some others had mentioned this same problem.

[john walker's workshop]

the barrier protects the cardboard from getting all warped and mushy, and redirects water back into the door so it will drain out, instead of allowing it to run down the panel into the carpets and interior. good idea to replace it. 3M spray glue and a trash bag opened up with a razor blade gets the job done. tuck the bottom back into the holes at the bottom of the door.

[autobonrun]

I hadn't considered the cardboard. I just bought a can of the 3M adhesive today to reglue some other parts. I'll put a barrier back in place. Thanks again.

[TerryH]

The term vapor barrier is a misnomer as it sounds like only vapor is going to enter the car if it's missing.

Some cars can be completely flooded without this shield to keep the water inside the door so it can drain out the holes at the bottom of the door. Each car make and model is different, but water does indeed enter the door and how the water falls depends on what it hits, what it clings to, and how the door was designed.

With the door panel off, use a garden hose without a nozzle. Get about a 2 inch stream and run it along the exterior belt line molding with the window up and door open. If any water leaves the door except through the drains, it will need attention. You also don't want water to splash on your cardboard door panels.

I have found the best replacement is some medium heavy plastic and a roll of 5/16" windshield tape (butyl tape).

[RSBob]

After I replaced the missing vapor barriers, the car really started to fog up on rainy days. Looks like I lost the flow through effect - but I'm sure the door panels appreciated it.

[randywebb]

OK, my favorite is visqueen and a caulk like "stickum"

Is anybody gonna post for Saran Wrap?

[ruf-porsche]

I use a "GLUE" stick to reattach the vapor barrier.

[jbrinkley]

fwiw pelican's got them moisture panels for pretty cheap, they line up good also. feel like a cross between wax paper and visqueen

[kqw]

Once you replace the plastic, when you close your car door, that solid sound is back.