closed cell foam vs polyfill

[fasfocus00 5,000+ posts]

polyfill and closed cell foam are the choices? i want to line the inside of a ported box. I have some left over closed cell foam from a poker table that I built. will the closed cell foam (1/4" thick) slow down the back wave like polyfill or will it just muffle/absorb the wave? or will it do something completely different?

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[Blue Fury 10+ year member]

I've read it just takes up volume. I've tried it and there was almost insignificant sound difference. It was just that little bit better without it.