RussB

A long time ago, I treated the inside of the left rear door skin of my 1988 5000CSTQ with Dynamat Xtreme. I recently removed the door's door panel to repair a broken lock mechanism and applied 3/8" thick closed-cell foam sheet (available inexpensively from insulation supply houses) while the door's innards were exposed. The foam sheet is black in color and easily cut to size with a pair of scissors.. I used a spray can of 3M interior trim adhesive to apply adhesive to the mating surfaces.

The first photo is midway during the job; I've applied foam sheet to the bottom section of the door. The second photo shows the top and bottom of the door skin covered with Dynamat Xtreme, which in turn is now covered with 3/8" thick foam sheet; the door is ready to be buttoned up.

This was the last door to have foam sheet applied over top the Dynamat Xtreme. I *think* that I can a hear a difference. In any case, the car is now very quiet and comfy.

I can drive at 50 mph with all of the windows open and still hear the stock radio just fine.

a-talk

Wow, you are really committed to quieting your car! Are you concerned about the foam getting wet at all? That'd be my only concern.

BTW, you filled the braces in the trunk with spray foam too, right? How much of a difference did that make?

RussB

This foam sheet is closed-cell: the walls of each cell are intact, so fluids such as water can't penetrate it. If it were open-cell (which would do a better job of absorbing sound) it would be vulnerable to water incursion and mildew inside the door. I'd use open-cell foam only if I were certain that it would never be exposed to water. In my car, all the foam sheet is closed-cell . . . mostly because it can be obtained at low cost from insulation suppliers.

I installed the Dynamat Xtreme panels and Great Stuff foam in the trunklid braces at the same time, so I can't tell how much only stiffening the trunklid braces with foam helped.

The only material of significant cost was the Dynamat Xtreme. Even that can be bought at less than 50% of list price on eBay. I think that Second Skin's Damplifier or Damplifier Pro may be better values. (When I began the project, the only product name I knew was Dynamat.)

a-talk

Right, I'd forgotten the whole closed vs. open cell thing. I may have to try this myself when I have my door panels off. I did use some damplifier (or something comparable, can't remember) on my passenger front door when it was open, but I can't say how much difference it made as I only did one door.

Thanks for the info man!