Best thin sound insulating material?
 

I have these nifty abs plastic door cards on my pickup, and the only problem with them was the fasteners that were provided with them since they tend to get brittle enough to break after five years or so if I need to remove the door card. I nabbed some nifty reusable clips that push-in/screw out but I still need about a quarter of an inch to get a snug fit. Initially I was thinking about going w/ some rubber washers, then I realized I would like a bit more sound insulation. What is the best and cheapest thin (~1/4") material I could use for sound insulation?

lead.

Ha! Isn't scrap lead like 10x the price of scrap steel? :flamethro

Of course. weight stops sound though and lead is pretty heavy.;)

Now if you want something practical look above!;)

Yikes! The dynamat looks like it would cost as much as the scrap lead anyway. ;)

I wonder if there are any open cell foams that can be bought on the cheap...

My old Ferrari had masonite in its door panels, wrapped in conolley leather of course. Inexpensive, heavy and sturdy.

Foamboard is cheap and available at Staples.

carpet underlay is good & cheap,I have lined truck & tractor cabs with it & it makes a big difference.

Do you have any experience with this product, would love to make my car quieter?

mass loaded vinyl, very dense

Jorn,
It depends on what sort of noise you are trying to get rid of.
The under hood pads reduce motor noise, fixing door seals helps with wind noise. A layer of underlay placed under the carpet, inside the doors & inside the panels near your feet reduces the tire road noise.

There is some spray on/roll on stuff used on boats,:

http://www.silentrunning.us/

hell with dynamat.depending on how far north you live,go to the lumber yard and get some frostguard.it's a roll of underlayment for roofs that go under shingles to prevent water from permeating up under the shingles on shallow pitched roofs.it is pretty much the same thing as dynamat but about 1/10th the cost.

What about "secondskin"? Seems to be a good price. My problem is vibration and rattle.