Took apart my doors to install some new speakers, and found the insulator material was completely trashed. By door insulator, I mean the clear/black plastic piece that seals between the door frame and panel.




Right now I am thinking about using some 6 mil plastic sheeting:
https://www.amazon.com/gp/product/B00KOOF5W0/
And applying it with either 3M spray adhesive or rope caulk, depending on which one seals best while still being removable.

Any thoughts on how to do this a bit better? That plastic sheeting is pretty thin compared to what was on there originally, and I'm wondering how much sound/thermal/material insulation is actually provided by the original part.

 

It's more of a vapor barrier to keep moisture out. If you want to quiet down the interior you can use a sound deadening insulation like Boom Mat or Dynamat. I lined the whole floor of my JK with sound deadening mat that had a heat reflective backing, it help a lot with heat and noise.

 

The MAJOR reason it's there is to keep all the rainwater from entering the cabin and destroying the stuff in the doors, like your speakers!