Originally Posted by AvB
The foam I used was about 30kg/m3, and I'm not sure how that compares with cubic foot! But it's about the lightest version available and expands to about 33x at maximum. However I used it at about 1/12th of the cavity volume, so it gets lots of back pressure and forms a nice even dense foam.
Converts to 2lb/cu. ft., definitely on the lower end of PU foam density in the hand-castable systems. Spray foam goes lower density but has lower physical properties fyi.