had a special on one show where a contractor was injecting slow and easy going foam into the crevices in the walls between the studs.
They bored a small hole in the wall between each set of studs. Then they had a nozzle like a gas pump one and stuck it in the hole and poured it in and stopped when the stuff came out the hole. Then moved to the next.
This was good, but it took many holes in the wall that had to be plugged up.