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Density vs R-Value for Common Insulation Materials

This is a plot from the ASHRAE Handbook of Fundamentals, 2005 edition, page 23.15:

The interesting thing (to me) is that at densities over about 0.6 lb/ft^3 fiberglass has a higher R value (lower conductivity) than cellulose. So, it looks like FG could be a significantly better insulation if it was installed at higher densities. It gets up to R4.5 per inch at 2.5 lb/ft^3 density.