We had the cathedral ceiling of an old bungalow spray foamed that I am restoring with my son.
We chose it because 8 or 9" of fiberglass in a large 2x10 ceiling does not meet code. They sprayed in about 5" of the stuff right onto the bottom of the old roof deck. It sealed all the cracks and crevices, and no need for a separate vapor barrier. The difference over the fiberglass was immediately noticeable, and a dramatic difference.
It got rid of all the drafts, no more heat radiating down from the ceiling. The house is noticeably less humid. The A/C is now two degrees lower, keeping the same comfort level.
We did have a big leak when a storm blew a section of paper off the roof before they got the new shingles on. The foam did not absorb water, which found its way down by the wall.
It is flexible and pliable.
2006 Safari SE FB
2000 F150 4.2L
2011 F250 6.2L