My understanding of the R value of cellulose is that it's about R 3.4 for dense pack and a little higher for loose fill. Loose fill is higher before it settles also. I'm getting this from Bill Hulstrunk, the engineer at National Fiber. Wouldn't surprise me if there were new evidence though. NF is less than 10 miles away from me so I've worked with Bill Hulstrunk on more than one occasion when building inspectors are being crotchety. Great guy and a great product. More fuzzy and less dusty than the stuff they have at Home Depot. Green fiber or something I believe it's called. The bag looks like a NF bag so I'm always fooled.
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