Polyfill

I have read and heard that putting Polyfill in the bottom of your sub box will make the sub think the box is bigger than it really is. I've heard up to 25% bigger. Is this true? Has anyone ever used this or heard of it working?
Thanks

there are many conflicting opinions about this subject. my suggestion, go out and buy some, it's really cheap, and try it out on your setup. then you'll have conclusive results and it won't matter what anyone has to say. good luck.

I'm currently building my fiberglass box so when I'm done I'll test it out because it will more than likely be smaller than the recommended enclosure size.

from my understandings, the polyfill effects the way the air moves, i.e. takes longer for it to bounce off the walls (if that makes sense). that is why it makes it "seem" bigger to the sub.