I've read a lot on sound deadening and sound absorption. I've applied Raamat to my doors and want to take the next step. People seem to suggest the PartsExpress acoustic foam, part #260-318 for in the doors. My question is when do you use open cell vs. closed cell foam? I can get different packing foams from the mail room in my company for free. How can you tell by looking at the foam if it's open or closed cell? Has anyone seen the thin pink packing foam that is about 3/8" thick, it's kind of shiny on one surface; would that be like the PE stuff? How about the egg crate stuff that they put in boxes; is that like the cheaper egg crate stuff you can put on the walls? Foam experts opinons wanted.

TIA

 

I would try the egg crate stuff. I have heard of people using it in home audio applications. Curious though, won't it get wet?

I live in Oregon, so mildew and mold are always an issue.

 

Carpet padding. Thats what I used and works great. The type I got was from Lowes and has a plastic sheet backing for moisture blocking. It was pretty cheap too.....

 

It's not difficult to tell open cell from closed cell if the cell size is large. If small it's a different story. Closed cell will not absorb water, or vapor. Open cell will. Which is better from a sound absorbtion point of view varies with frequency as well as other properties. The density of the foam probably affects the sound absorbtion properties as much as the cell structure. For insulation purposes closed cell would be better.

 

Also, open cell foam will be easier to squash when you put pressure on it. Closed cell foam will be more resilient and bounce back quickly. open cell will regain it's shape a little slower.

try squeezing a bit of water into it also... if it will absorb water, then it's open cell. if it stays on the surface, it's closed cell.


Either one will work in the car, but closed cell is easier to use.. When you use spray glue to apply it, the closed cell sticks better. open cell will come unglued over time and you'll have to glue it on again.

The carpet padding stuff is usually small chunks of open cell foam.. The smooth plastic backing is GREAT for spray glue adhesion though. once it's on there, it doesn't come off.
Problem with this stuff is that it's thin- about 1/2". doesn't damp sound much over thicker stuff.




Best thing I've found to use is 3/4" or 1" open-cell foam. again, the open-cell stuff is hard to keep stuck down, but it's damping properties seem to be a lot better for reducing road noise and other cabin noise.