Cellulose vs Foam
Cellulose Insulation vs Spray Foam Insulation
Foam insulation is very costly and can take decades to pay for its initially high installation costs before seeing any actual energy "savings" by its use.
Foam insulation requires special thermal barrier enclosing techniques by code to prevent fire acceleration adding to the cost.
Foam does not provide for complete insulation needs and does not address heat loss/gain via convention through framing members.
In short, foam will be your most costly way to insulate and will provide you with the least return economically and energy wise than using combinations of conventional insulations.
Dense-packed cellulose will not settle. That's why whenever cellulose is blown into a sealed framing bay (stud/rafter/joist, etc), it should be dense-packed.
When cellulose is loose blown, as in when blowing to cover an attic floor, it will settle over time. It eventually settles to its natural density.
Dense-packing blows packs the cellulose in at a density GREATER than it's natural settling density, therefore the cellulose will not settle anymore after installation.
Cellulose is a great insulating material, for when it is dense-packed the fibers knit together. It acts as an air infiltration barrier, it most certainly deadens sound, and it not only gives a higher R-value than FG, a much higher EFFECTIVE r-value than FG.
Cellulose will also absorb radiant energy. FG is transparent to radiant. That means that if you pack your rafter bays with it, you won't get a hot attic in the summer, as the cells block the radiant Ga in into the attic.
Cellulose also holds moisture better and longer than FG (that's a good thing) and then releases it during a drying cycle, minimizing potential harm to the framing.
You will need to install a dehumidifier in your house by using foam. Your house won’t “breath”.