Okay, this is a really technical question so I need a techical answer - don't spare me the physics!

To let you know what I'm doing, I'm sound proofing the entire car with a layer of sound barrier (loaded vinyl) above a layer of sound absorber (foam). So for a barrier I was looking at-

Mcmaster barium loaded vinyl (54665t22) STC=20. (.5lb/square foot which is as high as I want to go for weight reasons, ya know what I mean if I'm doing the whole car)

and then I came across this on foambymail.com's web site.

Volara FOAM STC=24! (i believe they are saying this is for 1/8" thick)

Does anyone see something strange here? Why is foam given an STC instead of an NRC? Barriers are usually given an NRC and foams STCs. Because if this foam has that good of an STC, there's no way I'll buy vinyl because it's hella more heavy and much more expensive, not to mention functions worse!

If nobody know the answer, maybe I'll buy both and sandwich it with closed cell foam below, vinyl center, volara foam top. But I don't know if all this will fit in behind panels and under the carpet.

K, I'm studying in the school library but I had to fool around on the computer for a bit... now back to the books, eeeesh

2gnt: '99 RS-T, killed by a toyota, pending rebuild...
Daily: Volt
Daily #2: '99 EVG ebike- STOLEN by PEDRO

got me there man, shoulda picked up a book on Materials of Engineering or Construction or something

jZa
IHS # fo-six-fo-six

"real men don't ride stick"

man, I almost have... I've gotten into so much depth here and it's only about foam, hee hee. I've emailed all these acoustic foam producing companies asking them about stc's and nrc's, and 1/2 the tie their service departments are like "sorry, we don't know the anwer... we're forwarding it to our chief engineer."

Correction of above(STC is for a barrier, NRC is usually for foam)

2gnt: '99 RS-T, killed by a toyota, pending rebuild...
Daily: Volt
Daily #2: '99 EVG ebike- STOLEN by PEDRO