his is to correct some information. Cellulose actually has a highr R per inch than cellose (abour 3.65 per inch). Although the high density fiberglass batting is at this level, standard batting is only about R-3.0 per inch & blown fiberglass is a dismal R 2.4 per inch. Therefore, to have an R-38 insulation you need 12" of fiberglass batting, 16" of blown fiberglass, or 10" of blown cellulose.
In dense pack cellulose or wet spray (which appears to be what is being discussed), even though it is compressed, mainains an R of about 3.55 per inch. When compressed, cellulose has the added advantage of virtually elliminating air leaks providing a more consistant or True R-value. Some studies show fiberglass losing much of it's effectiveness because of convection (one I saw stated that a 2X6 wall w/ R-19 fiberglass actually was only performing a R- 11-13.